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The principle adopted is that of condensing moisture upon the inside of a polished cylinder the outside of which has been cooled. This instrument described in the Journal de physique, April, 1883, consists essentially of a brass cylinder, nickel plated, and highly polished on the inside, provided with two fine tubes near its ends. Through one of these, by means of a rubber tube conducted to the exterior air or to any point at which it is desired to obtain the hygrometric state, the air is drawn into the polished cylinder by using an aspirating-bulb attached to the other. At the first extremity is placed a ground-glass plate, which permits light to enter. This light appears as a bright annulus enlarged three times, as viewed by a magnifier at the other end.

The cylinder is supported in a box, through the centre of which it passes horizontally. This box is provided with two openings, as in an ordinary condensing-hygrometer, through which, by aspiration or by blowing, ether contained in the box may be evaporated, thus lowering the temperature, which is indicated by a properly adjusted thermometer.

In observing, air is drawn into the cylinder by an aspirating-bulb, and at the same time the ether is evaporated. The moment dew appears on the inside of the cylinder, which is easily seen, the reading of the thermometer gives the dew-point. This may be readily obtained again and again with an error less than 0.1° C., or 0.18° F.

Some of the advantages claimed, are the possibility of guarding against varying air-currents; the delicacy of adjustment; the ease and accuracy of observation with the magnifier; the easy manipulation of a uniform light, so difficult to obtain in the ordinary form; and the use of the apparatus in the house for determining the dew-point of the outer air.

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In regard to the last advantage claimed, it may be said, that if accurate results can thus be obtained when the air-temperature is from -40° to - 60°, or when there is a difference of forty or more degrees between the air-temperature and the dew-point, the instrument will be of great service; but there should be some means of aspirating the outside air through the ether, and the apparatus should be very carefully isolated by non-conductors of heat, as the heat of the room would make a sufficient cooling impossible under the conditions just named. The possibility of easily securing such isolation without interfering with the working of the apparatus seems the most important advantage to be derived from its use. H. A. HAZEN.

THE RIGHT WHALE OF THE NORTH ATLANTIC.

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THE four plates devoted in Dr. Holder's recent paper on this subject to the external and osteological characters of the right whale of the North Atlantic (Balaena cisarctica Cope B. biscayensis of European cetologists), and the seventeen pages of text descriptive of the same, form a welcome and valuable contribution to the history of a species possessing peculiar interest. Its habitat being the temperate waters of the North Atlantic, extending from the coast of Florida and the Bay of Biscay, northward to southern Labrador and Iceland, it was pursued off the coast of Europe for centuries before the Greenland whale (B. mysticetus), the basis of the great northern whaling industry of modern

1 Bull. Amer. mus. nat. hist., vol. i. no. 4, pp. 99-137, pl. x. xiii., May 1, 1883.

times, became known to Europeans. It was hunted by the Basques and Norwegians as early as the ninth and tenth centuries, was the basis of the whale-fishery of the fifteenth and sixteenth centuries, and was already approaching extinction in European waters, when the great arctic or Greenland whale first attracted the attention of whalers, early in the seventeenth century. The latter, from its greater size, easier capture, and larger numbers, its greater yield of oil and superior quality of baleen, became at once the chief object of pursuit; and the earlier known species was quickly lost sight of as a commercial animal, except on this side of the Atlantic. Here it was the species chiefly hunted by American whalemen down to about the middle of the last century, when from its rarity its pursuit was gradually abandoned for that of the arctic species. The cisarctic animal was early known to the French as the 'sarde;' to the Norwegians, Dutch, and Germans, as the 'nordkaper;' and to the Icelanders as the 'sletbag.' To Americans it was known under the various names of northcaper,' 'Grand Bay whale' (in reference to the Bay or Gulf of St. Lawrence, where it was chiefly hunted), 'seven-foot-bone whale,' and 'black whale.' Under these names it was briefly described by various early non-scientific writers, and, in the works of the early systematists, was very inadequately characterized under various systematic names. It is the Balaena glacialis of Klein (1741) and Bonnaterre (1789), the B. islandica of Brisson (1756), and the B. nordcaper of Lacépède (1804). It was, however, practically unknown to science, till the researches of Eschricht and Reinhardt, published in 1861, led to its rediscovery, having been, until then, generally confounded with the B. mysticetus. During recent years it has several times been taken off the coast of southern Europe and in the Mediterranean. These specimens have formed the basis of important memoirs, and given rise to additional specific names. It is, however, now commonly known in Europe as Balaena biscayensis, the name originating really with Gray, although almost universally ascribed to Eschricht, who merely designated the species by an equivalent vernacular name. It was redescribed by Cope in 1865 as B. cisarctica, from a specimen taken at Philadelphia, the skeleton of which is now in the museum of the Philadelphia academy of natural sciences. Ruling out the name 'islandica' of Brisson, on the ground that it antedates the binomial system, and 'glacialis' of Bonnaterre as untenable from its misleading tenor, we have left, of the earlier names, nordcaper' of Lacépède, which is objectionable only from its barbarous character, but no more so than hundreds of other names currently employed in zoology, save by a few purists who admit nothing that is unclassical.

Dr. Holder describes and figures, 1°. The external characters of a male specimen taken off the NewJersey coast in the spring of 1882; 2°. The skeleton of a specimen (sex unknown) stranded some years since on Long Island; 3°. Through notes furnished by Dr. G. E. Manigault, a specimen captured in the harbor of Charleston, S.C., in January, 1880. Professor Cope's specimen, and two of the three here mentioned, are more or less immature. There is, however, the skeleton of a fully adult example, taken at Provincetown in 1865, in the Museum of comparative zoölogy, of which, as yet, no description has been published. The New-Jersey example not having been preserved, there exist at present four skeletons of this species in American museums. Holder figures the skull of the Charleston, the external characters of the New-Jersey, and the

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skeleton of the Long-Island specimens, and gives measurements and details of the external characters and osteology, all of the highest importance; our only regret being that he did not, respecting some points, make fuller use of his opportunities. We wish we could speak with equal satisfaction of the historical portion of his paper, comprising one-half of his text. Besides numerous outrageous typographical errors (a part of which, however, are corrected on an errata slip), relating to proper names and titles of works (Researches and Reserches' for 'Recherches,' 'Seibold' for 'Siebold,' Van Benedin' for Van Beneden,' both the latter in repeated instances, and various others of like character, are among those still uncorrected), there are errors of statement of so grave a character as to require notice. It would seem, for instance, that only the merest novice in cetology could have been misled into supposing that the quotation given at p. 114, respecting a whale captured far up the St. Lawrence River in August, 1871, and reported as 'Balaena mysticetus,' was any thing but a rorqual or finback whale (in all probability, Balaenoptera musculus), much less into an attempt to explain away the evident discrepancies to make it referable to the North Atlantic right whale; yet we find our author devoting several pages to an attempt at this absurdity. Again: in the strictures passed upon Scoresby (pp. 121, 122), he informs us that "his [Scoresby's] inability to portray the subject pictorially was a misfortune," and that "he furnished to science an incorrect figure, at second hand," of the B. mysticetus, and considers it 'deplorable' that "nearly every book published to this day, having an illustration of B. mysticetus, shows a manifest copy of Scoresby's figure." That it was the best figure, if not quite correct in all points, of the species down to 1874, when Scammon's admirable illustration was published, has, I think, hitherto been unquestioned; and if our author has evidence that Scoresby's figure (or rather figures, for he gives two) was not original, its presentation would be undoubtedly a revelation to cetologists. That our critic of Scoresby is none too familiar with Scoresby's cetological writings is evident from his statement, that Godman (p. 129) "gives a lengthy account of the mysticetus, with an amount of anatomical and physiological knowledge of the subject quite unusual;" the fact being, that Godman's account is an unaccredited compilation from Scoresby, whole pages being taken entire, and without change, from Scoresby's work, particularly in his notice of the whalefishery. Bachstrom's figure, published by Lacépède as representing the nordcaper, and which is accepted by Dr. Holder as such, recent eminent authorities have unreservedly referred to B. mysticetus; yet on its interpretation as a representation of the nordcaper rests much of Dr. Holder's criticism of Scoresby. We are surprised to see no reference to the various recent original memoirs relating to the so-called B. biscayensis, either in the author's formal notice of the Right whale of Europe' or in the bibliography of the general subject given at the end of the paper. In the list of works referred to' the uncorrected errata are numerous; J. C. Gray' (four times repeated), for example, standing for J. E. Gray, Col. Hamilton' (also on p. 129) for 'W. Jardine,' etc., while there are also inaccuracies of dates. While, as above said, Dr. Holder gives us valuable information about the external appearance and osteology of the North Atlantic right whale, his historical résumé is seriously defective and misleading. J. A. ALLEN.

FIG-INSECTS.

FEW insects offer more remarkable structural peculiarities, or have more puzzled systematists, than the minute Hymenoptera associated with the caprification of figs. Part I. of the transactions of the London entomological society for 1883 opens with a very interesting illustrated paper by Sir Sidney S. Saunders, descriptive of fig-insects allied to Blastophaga from Calcutta, Australia, and Madagascar, with notes on their parasites and on the affinities of their respective

races.

It is chiefly as a contribution to the discussion of the affinities of these insects that Mr. Saunders's paper possesses so great an interest. In the transactions for last year, Westwood, by certain authoritative statements, appeared to settle the place of the fig-insects (at least, for the genus Sycophaga) as among the Chalcididae, and not far from Callimome. He remarks, "The structure of these fig-insects, especially as shown in the females (whose character must be shown as more truly normal than that of the males), recedes so entirely from that of the Cynipidae that we cannot for a moment adopt the suggestion that the fig-insects are Cynipidae... Hence M. Coquerel had no hesitation, in describing the female of one of his fig-insects, to give it the name of Chalcis? explorator; and it is impossible to compare his figure of that insect, or mine of Sycophaga crassipes, with a female Callimome, and not be convinced that the fig species are most closely related to Callimome (many of the species of which are parasitic upon the gall-making Cynipidae). The structure of the antennae (even to the minute articulations following the second joint), the fusion of the three terminal joints of these organs, the structure of the wings and wing-veins, and the long exserted ovipositor, sufficiently prove that these insects must be placed in the great family Chalcididae."

Mr. Saunders differs from Westwood in these conclusions, showing that the place of the whole group must not be considered in so sweeping a manner. He disposes of the relationship of the group to Callimome by the following points: 1. The minute articulations in the antennae of the female Sycophaga do not correspond with any in the same sex of Callimome, nor do they occur in Blastophaga, the antennae of which also differ in other respects from Callimome. 2. The fusion of the three terminal joints, while found in Sycophaga, does not occur with Eupristina nor with Agaon. 3. The wing-veins differ inter se among the fig-insects, and Callimome does not coincide with Eupristina in this respect; moreover, the wings are invariably absent in the males of the figinsects. 4. The ovipositor of fig-insects varies in length, and always maintains an arcuate position. The argument which Westwood brought up in a later paper, of the similarity of the dentate genital claspers of Sycophaga to those of Platymesopus and other Chalcids, Saunders disposes of by saying that this character can have no tribal value, as it is found alike in Sycophaga and several of its parasitic associates; moreover, this character is not present in Callimome.

Mr. Saunders's final conclusion is, that this anomalous group which he calls Sycophagides should be placed under the Cynipidae in the following man

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OPTICAL RESEARCHES ON GARNET.

IT has been for a long time known that all garnets, as well as some other isometric minerals (boracite, analcite, alum, senarmontite, etc.), do not show the action on polarized light which would be required by substances crystallizing in the isometric system; and to find out the causes of these optical variations, and the laws which govern them, C. Klein has examined (Jahrb. min., 1883, 87) as many as three hundred and sixty different garnet sections, cut parallel to different crystallographic planes, and from various localities. His researches do not indicate that because garnets frequently show these optical variations we should refer them to some system of crystallography other than the isometric; for garnets from the same locality often show a great variation in optical properties, some crystals being isotrope throughout, others in part uniaxial or biaxial. Others, on the other hand, have tried to explain the optical variations by regarding the various isometric forms as made up of numerous prisms, either uniaxial or biaxial, united at the centre, and whose bases make up the external crystal faces. Others regard the garnet substance as triclinic, and the various optical properties as the result of repeated microscopic twinning of the same.

The chemical composition does not influence the optical structure of the crystals, because the same optical phenomena are observed in garnets of different composition; and in garnets of the same composition, but with different form, varying optical structures are observed, even among crystals from the same locality. The form, however, in which the various garnets occur, governs the optical structure. Thus, in the octahedral garnets from Elba, what is called the octahedral structure is noticed. A section from this garnet cut parallel to an octahedral face, examined in parallel polarized light with crossed nicols, shows a triangular centre, which remains dark, and three fields on either side, which are alternately dark and light as the section is turned, being dark when one of the sides of the triangle becomes parallel to the plane of either of the nicols. In convergent polarized light, the centre shows the dark cross of a uniaxial crystal, while from each of the three sides a dark bar runs out into the side-fields at right angles to the edge. This indicates a crystalline structure made up of eight uniaxial prisms united at the centre of the crystal, and whose bases form the eight faces of the octahedron. A section cut near the centre of the crystal shows six of these prisms radiating out, while the upper and lower ones have been, of course, cut away. What is called the dodecahedral structure is observed on pure dodecahedrons. A section cut parallel to a dodecahedral face shows, in convergent polarized light, the appearance of two optic axes whose plane lies parallel to the longer diagonal of the rhomb. The tetragonaltrisoctahedral structure observed on crystals of that form shows, in sections parallel to the trisoctahedron faces in convergent polarized light, the appearance of two optic axes with very slight divergence, indicating a crystalline structure made up of twenty-four nearly uniaxial prisms united at the centre, and whose bases are the faces of the trisoctahedron. The plane of the optic axes is normal to the symmetry diagonal of the trisoctahedron face. In the hexoctahedron structure the sections show a biàxial structure, and the plane of the optic axes is very variable. By making and examining artificial gelatine crystals, the author was able to imitate many of the optical variations; and these seemed to be related to a contraction

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The elements of the earth's crust are the mineral masses (masses minérales).

The mineral masses, regarded from the point of view of their nature, take the name of rocks. Considered from the point of view of their origin or mode of formation, they are to be called formations. a. Stratigraphical divisions.

Regarded from the point of view of their age, mineral masses may be subdivided according to the following rules:

1. The word group (groupe) is applied to the three or four great divisions. Ex.: Secondary group. 2. The divisions of the groups are designated by the word system. Ex.: Jurassic system.

3. The divisions of systems of the first grade are designated by the word series (série), or by the terms section or abtheilung. Ex.: Lower oolitic section or series.

4. The divisions of systems of the second grade are designated by the word étage, or by the corresponding terms, piano (Italian), viso (Spanish), stage (English), stufe (German), etc. Ex.: Etage bajocien.

5. The divisions of systems of the third grade are designated by the term assise, or by its strict equivalents in the different languages. Ex.: Assise à A. Humphresianus.

6. The French expression couches (beds) may be employed as synonymous with assise.

7. A certain number of assises combined will bear the name of substage (sous-étage).

8. The first element of stratified masses is the strate or couche, schicht (German), stratum (Latin and English), strato (Italian), retek (Hungarian).

b. Chronological divisions.

9. The word era (ère) is applied to the three or four great divisions of time, corresponding to the groups.

10. The length of time corresponding to a system will be rendered by the word period (période).

11. The length of time corresponding to a series (section, série, abtheilung) will be expressed by the word epoch.

12. The length of time corresponding to a stage (étage) will be expressed by the word age.

II. Colors and signs.

1. Crystalline schists, rose-carmine (by preference); bright rose for the rocks of pre-Cambrian age; pale rose for those of indeterminate age.

2. Primary group. Decision referred to the committee of the map of Europe.

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4. Tertiary group (cenozoic), yellow, using lighter shades as the beds become more recent.

5. Quaternary deposits. Decision referred to the committee of the map of Europe.

6. Resolutions of detail relative to shades, reserves, etchings, and letter notations.

III. Rules concerning the nomenclature of species.

1. The nomenclature adopted is that in which each animal and plant is designated by a generic name and a specific name.

2. Each one of these names is composed of a single Latin or Latinized word, written according to the rules of Latin orthography.

3. Each species may present a certain number of modifications, related to each other in time or in space, and designated respectively under the name of mutations or of varieties. The modifications whose origin is doubtful are simply called forms. The modifications will be indicated, when requisite, by a third term, preceded, according to the case, by the words variety, mutation, or form, or the corresponding

abbreviations.

4. The specific name should always be precisely designated by the indication of the name of the author who established it. This author's name is to be placed in parentheses when the primitive generic name is not preserved; and in this case it is useful to add the name of the author who changed the generic name. The same disposition is applicable to varieties elevated to the rank of species.

5. The name attributed to each genus and to each species is that under which it has been primarily designated, provided the characters of the genus and the species have been published and clearly defined. Priority will not be carried beyond Linné's Systema naturae, 12th edition, 1766.

6. In future, for specific names, priority will be irrevocably acquired only when the species shall have been not only described, but figured.

LETTERS TO THE EDITOR.

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A powerful direct vision spectroscope. Ar a journal meeting in which Professor Rowland and the students of physics take part, an article came up for discussion which needs correction. In Comptes rendus, April 9, 1883, Ch. V. Zenger, in a note entitled Spectroscope à vision direct très puissant,' claims a dispersive power equal to that of thirteen sulphide-of-carbon prisms of 60° angle for a spectroscope composed of a parallelopiped of two prisms, one of quartz, and the other of a mixture of ethyl cinnamate and benzine, combined with a third prism of crown glass of angle of refraction 27° 13'. He gives as the angles the three rays make with the perpendicular to the last prism after they have passed through,

A

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H

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It will be easily seen that H should be negative in place of positive; which will make the dispersion between A and H 47° 5', in place of 132° 55′ which the writer gives. H. R. GOODNOW.

Johns Hopkins university.

Connecticut minerals.

The towns of Middletown, Portland, Haddam, and Chatham, in this state, have long been famed as a region remarkable for the number of minerals occurring in the veins of coarse granite. Within the last few days two minerals have been discovered in these veins, which, so far as I am aware, have not previously been reported.

Torbernite has been found at Andrus' Quarry, near the boundary between Portland and Glastenbury, associated with autunite, the occurrence of which has been previously reported.

Rhodonite has been found at the White Rocks in
Middletown.
WM. NORTH RICE.

Wesleyan university, Middletown, Conn.
June 9, 1883.

Book reviews.

I wish to quarrel a little with the critic of Gage's 'Elements of physics' in your issue of June 8, p. 517, for not keeping the following promise, found in the 'Prospectus of SCIENCE for 1883: "To promote one of its chief objects, and as a distinctive feature of the journal, SCIENCE will give its hearty support to those who are endeavoring to introduce the study of the natural and physical sciences into public and private schools, by drawing attention in every possible way to the high importance of this measure, as well as by giving illustrated articles, plainly worded, prepared by skilful hands, to guide the efforts of the teachers." He has failed to keep this promise by failing to give such information about the book he reviews as those who are endeavoring to introduce the study of physical science into public and private schools" would like to have. Many teachers cannot afford to buy every text-book they see advertised, and therefore must needs trust to reviews to tell them enough of a book to enable them to decide whether it is worth purchasing. In regard to a work on physics, they wish some such questions as the following answered:

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1. What is the plan of the book? Does the author expect the pupils to do experimental work, or that the teacher only will perform experiments? 2. If the author wrote with the view of having experiments performed by the pupils, how well has he succeeded in executing his plan? Has he succeeded in giving such experiments as will be of real service in laying the foundation of scientific work, and as can be performed in the short time that teachers in high schools and academies have for such work? Could pupils manage the experiments without the aid of a teacher? 3. Does the author give any directions in regard to preparing apparatus? If so, are these directions sufficiently exact and minute to enable an inexperienced person to follow them without trouble?

All of these questions a teacher would like to find answered in the review of a new book on physics. All the information he would get on these points from the review of Gage's book is found in this sentence: "The book is of merit as giving many experiments with apparatus of easy make." The reviewer said more than this, of course; but this one sentence is all to answer such questions as I have asked above. He was probably right in what he did say, which makes it the more to be regretted that he did not go farther. My quarrel with him is, that he did not say enough; that he did not say as much as your readers had a right to expect, certainly not enough for those readers who had not seen the book, and wished to know whether it was worth buying. This suggests a question. Are reviews written for the benefit of

those that have made the acquaintance of a book, or for those that have not? For myself, I can answer that I care most for the reviews of those books that I have not seen. In conclusion, I wish to say that Mr. Gage is a stranger to me, and I have never had any sort of communication with him. Whatever one might say in his behalf, my remarks were not made for his benefit, but to point out what I believe to be one of the first duties of the reviewer of a scientific book to his readers. S. T. M.

Lexington, Va., June 13.

[The limited space at our command will not allow of extended analyses of the many text-books of science which are continually appearing. A short notice

either of their general merit or demerit is all we can give. In the case of Gage's 'Elements of physics,' the reviewer used the book as a text to preach against the common custom of teachers in using the atomic theory in their explanations as if we knew definitely that atoms exist.]

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Solar constant.

Prof. C. A. Young has kindly called my attention to an unintentional oversight in my article entitled Solar constant' (SCIENCE, p. 542). In the general equation sent me by him, t represents 'degrees of heat,' not 'quantity of heat;' and m represents 'time,' not ' unit of time.' H. A. HAZEN.

A zoo-philological problem.

On the New-England coast, where Mya arenaria is abundant, and known as the 'clam,' an annelid which is common in the same localities is called the 'heclam,' and is believed by many fishermen to be the male of the mollusk.

In Norway, Mya arenaria is abundant in the fiords of the north. It has no economic uses; but its associate, an annelid, the 'pür' (said to be Arenicola piscatorum), is an important bait, and gives its name to the Mya which is called the 'pürschaal.'

Why should the common annelid and the common mollusk be thus associated in popular nomenclature in remote regions? It is interesting to observe that the form possessing commercial value in each instance gives its name to the one which is in lower G. BROWN GOODE.

esteem.

The sun's radiation and geological climate. In my objecting (SCIENCE, p. 395) to the assumption that the dissipation of solar energy from loss of heat diminishes the supply of sun-heat received by the earth, I said, that, so far as there has been any change in the supply, it has been in the direction of an increase, and hence cannot explain the undoubted decrease in the temperature of the earth's atmosphere. I think Professor Le Conte's criticism (SCIENCE, p. 543), taken in its entirety, corroborates my position. He shows that the quantity of heat incident normally on a unit of surface in a unit of time varies as the area of a great circle of the sun X heat-emitting power of each physical point of the sun: hence the quantity emitted would not increase, unless the heatemitting power increased faster than the square of the temperature. He adds that "some physicists (Rossetti) make the latter proportional to the square of the absolute temperature, while others (Stephan) make it as high as the fourth power." If Rossetti is right, there has been no decrease in the amount of solar heat received; while, if Stephan is right, there has been a very great increase: for, on the assumption that the temperature is inversely as the radius, as stated in Professor Newcomb's article (Popular

astronomy, p. 508), the heat-emitting power, if the solar radius is reduced to one-half, will be increased four times, and will just compensate for the great circle being reduced four times in area. If the emissive power increases, as Stephan claims, then a doubled temperature will increase it sixteen times, and, the area being diminished only to one-fourth, the earth will receive quadruple the heat.

It is true that the heat-emitting power of any (solid) body varies according to the area of its surface, providing all the other conditions are unchanged. In case of solids and liquids, very little change can be made in their density by any force that we can apply,

so little, indeed, that no appreciable effect can be produced; but gases are easily affected, and there is no difficulty in conceiving them reduced many times in bulk. Now, suppose two spheres, e.g., of hydrogen, of equal masses and of the same temperature, but one having twice the radius of the other. They will radiate equal amounts in equal times, as I shall try to show. I assume that the radiation goes on only from points of matter, the atoms of the hydrogen. Conceive each sphere made up of a vast number of concentric layers, each one molecule thick. The number of layers will be the same, and the number of molecules in each will also be the same: consequently the heat-emission of the outside layer will be the same in both spheres. What would be true of the first layer would be true of all, unless the outer one intercepts some of the rays. So far as the outer layer is gaseous and elementary (it is very doubtful whether any chemical compounds can exist in the intense heat of the sun), it is a vacuum to radiant heat; for Professor Tyndall, in Heat considered as a mode of motion,' has shown (p. 362) this in reference to oxygen, hydrogen, nitrogen, and air, and, in general (see rest of the lecture), that elementary gases or vapors produce little or no effect upon the radiant heat that passes through them. It must be remembered, too, that the source of heat employed in his experiments was icy-cold in comparison with the sun, and that the penetrating power of heat-rays increases as the temperature of their source rises. It is therefore probable that the heat from the lower layers passes through the upper ones, so far as they are gaseous, with little or no loss, and hence that in gaseous bodies the heat-emitting power for any given temperature is proportional, not to the surface, but to the mass or density.

But suppose that diffused through the upper layers were molecules that were capable of stopping every ray that impinged upon them. Neither the absolute number nor the size of these bodies would be affected by shortening the radius, but only the space between them. If the radius were reduced to one-half, the apertures would, be reduced in area to one-fourth, while the radiating molecules within any given distance would be increased eightfold: in other words, the chances of not passing out into space would be increased only four times, while the number of shots would be increased eight times; so that, in this case, the heat-emissive power would be actually increased by the condensation. If to this be added an increase of the same power from the rise of temperature (either as the square or the fourth power, Rosetti or Stephan), there can, I think, be no doubt that any change which has occurred in the earth's temperature from the sun's losing energy has not been in the direction of growing cooler.

As a corollary of the above, I add, the radiant or heat-emitting power of a sphere of gas appears to be a function of mass and temperature, and not of surface and temperature.

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