« AnteriorContinuar »
HIS EPOCH OF GREATEST FERTILITY.
The work on meteorology was published in September, 1793. Dalton had come to Manchester in the spring of that year. He was now twenty-seven years of age. The removal to an active town seems to have satisfied his cravings for a larger sphere of labour which were forcing him from his attachment to his neighbourhood. He was self-taught, a raw countryman, in many respects rather rough in his acquired habits, although of a naturally gentle disposition. Such a distance from active life would have made many men idle, such a sudden entrance into it has often the same effect on others. Neither seemed to affect him, there was little change of habit, he was still in the streets of Manchester as on the hills of Cumberland, the active observer and thinker. On October 3rd, 1794, he first appears as a member of the Literary and Philosophical Society of Manchester, having been proposed by Thomas Henry, Dr. Percival, and Robert Owen, the veteran enthusiast who would willingly compel all mankind to be reformed by his simple formula. On the 31st, he read his first paper to the society, an event to him of great importance, greatly influencing all his future life, as he soon after became the representative of that body, continuing so for the remainder of his life.
This paper was entitled “ Extraordinary Facts relating to the Vision of Colours." * He says there, p. 30,
“ It may be proper to observe, that I am shortsighted. Concave glasses of about five inches focus suit me best. I can see distinctly at a proper distance; and am seldom hurt by too much or too little light; nor yet with long application.”
* Memoirs of the Philosophical Society of Manchester. Vol. V., p. 28.
“ I found that persons in general distinguish six kinds of colour in the solar image ; namely, red, orange, yellow, green, blue, and purple. To me it is quite otherwise; I see only two, or at most three, distinctions; these I should call yellow and blue, or yellow, blue, and purple. * My yellow comprehends the red, orange, yellow, and green of others, and my blue and purple coincide with theirs.”
He sums up the peculiarities of the vision of himself and others who have been found similarily affected thus; p. 40.
51. In the solar spectrum three colours appear-yellow, blue, and purple. The two former make a contrast; the two latter seem to differ more in degree than in kind.
2. Pink appears, by day light, to be sky-blue a little faded; by candle light it assumes an orange or yellowish appearance, which forms a strong contrast to blue.
3. Crimson appears a muddy blue by day; and crimson woollen
is much the same as dark blue. 4. Red and scurlet have a more vivid and flaming appearance by candle light than by day light.
5. There is not much difference in colour between a stick of red sealing wax and grass, by day.
6. Dark green woollen cloth seems a muddy red, much darker than grass, and of a very different colour.
7. The colour of a florid complexion is dusky blue.
8. Coats, gowns, &c., appear to us frequently to be badly matched with linings, when others say they are not. On the other hand, we should match crimsons with claret or mud; pinks with light blues ; browns with reds; and drabs with greens.
9. In all points where we differ from other persons, the difference is much less by candle light than by day light.”
He found several persons having the same peculiarity of vision, and says (p. 43), “ It appears, therefore, almost beyond a doubt, that one of the humours of my eye, and of
the eyes of my fellows, is a coloured medium, probably some modification of blue.”*
Although this paper was an observation on himself, it is in reality a discovery; the facts had not been arranged before he arranged them, and found out other persons similarly situated. A peculiar keenness of reasoning was needed to find it out, as we must remember that with such persons there is little community of feeling on colour, and scarcely a mode of judging whether they see any colours exactly as the normal eye does. It would probably explain many strange occurrences if we were to consider that there are really persons in the world who see all crimsons as 66 dark blue” or “a muddy blue," and who would “match crimsons with claret or mud; pinks with light blues; browns with reds; and drabs with greens ;” who see the healthful tints of a florid complexion to be like “ dilute black ink on white paper,” or
or “a dull opake blackish blue, upon a white ground." How many strange mistakes and visions might be accounted for by this defect of sight. A fair face with glowing veins would be to Dalton as a corrupting corpse. But it may be said that custom would make all appear as well to him as to others; no, it cannot be so: a defect must constantly carry with it the consequences of a defect, and in this case the established difference which nature has made between life and death, beauty and horror, was hidden from the eye, and therefore to a great extent must have been concealed from the intellect. To this cause partly we may refer that want of fine sensibility to external things which peculiarly marked his scientific as well as social life.
Dr. Whewell has called such persons idiopts, because their vision is peculiar; this is not sufficiently characteristic, and as has been remarked sounds badly, Sir John Herschel having changed it to Dichromic vision, believing that one of the three colours is lost to the eye entirely. Such a vision there seems to be, but this extent has not been observed in any instances, by Dr. George Wilson, who thinks that there is no colour quite lost, although the power of perceiving be feeble, and he names it Chromato-Pseudopsis, or a false vision of colours. This he has translated by Sir D. Brewster's term, colour-blindness, which appears much too strong when we consider that some colours are well seen, and others seen in part. It seems, in fact, to be an imperfection in the power of distinguishing colours, which may exist to any extent, either very slightly, as is seen in every-day life, where, for example, among the many workpeople in a large mill, only a few are found fit for arranging yarns with accuracy. A nice perception of colour is there a valuable gift, and is paid for accordingly. Or it may occur decidedly defective, as with Dr. Dalton and others. Dalton's brother had the same defect, and one or two others in the neighbourhood of Eaglesfield, of whom I have lately heard. It is probable that there are many gradations, beginning with deficient colour sight and ending in Dichromic, or perhaps Monochromic or Achromic vision, or true colour blindness. Dr. Wilson well remarks, that Daltonism, under which it has been known, is not a proper name for the peculiarity, as it connects his name with a defect. Indeed few eyes are found equal to Dalton's, if we judge of them by their results. Dr. Wilson has made the remarkable discovery that this defect may almost be called common.
* Mr. J. A. Ransome, who examined the eye after death, found nothing whatever to account for the peculiarity of vision. Certainly colours appeared as usual through it. He believed that the cause was a deficient sensorial or receptive power.
Dalton remained without giving anything to the public until 1799. In the College his order showed itself in the careful list of students and their lessons, still remaining. Possibly his duties occupied too much of his time to allow of experiment, but he comes out so suddenly after that as physikist and chemist, that his time must have been spent
in suitable studies. On March 1st, 1799, he read to the
2. Of the quantity of water that flows into the sea.
4. Of the origin of springs.” The first three are accompanied by experiments, but there is a looseness in the calculations which renders the paper rather like a sketch of the subject. He, however, collects a great deal of information as to the annual fall of rain in various places, and in a note explains clearly, as before alluded to, his ideas as to the state of aqueous vapour in the air. The looseness of expression is not at all times with him an indication of want of decision, but his peculiar style of writing, as if every one knew the subject, and were ready to draw out his reasoning into all its details, as soon as expressed. His experiments, begun with the hand, seem often finished with the head, so rapidly are his conclusions come to, and the natural law established in his mind. Even now we can add little to the relation between evaporation, rain, and dew, and on the origin of springs he is clear, quick, and decisive, saying that they come from the rain. This subject had been much disputed; filtration from the sea having been a favourite method of obtaining the water, as well as subterranean reservoirs like those of Father Kircher, who shows them in engravings continually boiling out from the centre of the earth. Dalton was not the first to suggest the explanation, of course, but the subject was sufficiently uncertain to call for elucidation. On April 12th,
* Memoirs of the Literary and Philosophical Society of Manchester. Vol. V., p. 346.