observation ;-an enlarged sphere of chemical phenome acquaintance with a far greater number of individual than were then known; from the properties of which, a those of their combinations, tentative approximations to principles might at first be deduced; to be confirmed or ed, enlarged or circumscribed, by future experience. have retarded the progress of science, and put off, to a tant day, that affluence of new facts which Priestley so accumulated, if he had stopped to investigate, with pair rigid precision, all the minute circumstances of tempera specific gravity, of absolute and relative weights, and of line structure, on which the more exact science of our ow is firmly based, and from which its evidences must hence be derived. Nor could such refined investigations ha been carried on with any success, on account of the in tion of philosophical instruments. It would have been fi also, at that time, to have indulged in speculations respect ultimate constitution of bodies ;-speculations that have ground-work, except in a class of facts developed within thirty-five years, all tending to establish the laws of comb in definite and in multiple proportions, and to support more extensive generalization, which has been reared genius of Dalton.

It was, indeed, by the activity of his intellectual fa rather than by their reach or vigour, that Dr Priestl enabled to render such important services to natural s We should look, in vain, in any thing that he has achiev demonstrations of that powerful and sustained attention, enables the mind to institute close and accurate compariso to trace resemblances that are far from obvious;-and criminate differences that are recondite and obscure, Th logies which caught his observation lay near the surface were eagerly and hastily pursued; often, indeed, beyon boundaries within which they ought to have been circum ed. Quick as his mind was in the perception of resembl appears (probably for that reason) to have been little a ed for those profound and cautious abstractions, which s

1

11 C

omena;-an dual bodies, h, and from s to general d or correcte. It would

to a far disy so rapidly painful and perature, of d of crystalur own times enceforward s have then be imperfeceen fruitless, especting the have no solid

thin the last combination port the still ared by the

ual faculties, Priestley was tural science. achieved, for ention, which mparisons;-and to dise. The ana

surface, and beyond the circumscrib resemblances,

little adaptwhich supply ber, patient,

the Philosophical Character of Dr Priestley.

7

others, who, though far less fertile than himself in new and happy combinations of thought, surpassed him in the use of a searching and rigorous logic; in the art of advancing, by secure steps, from phenomena to general conclusions;—and again in the employment of general axioms as the instruments of farther discoveries.

Among the defects of his philosophical habits, may be remarked, that he frequently pursued an object of inquiry too exclusively, neglecting others, which were necessarily connected with it, and which, if investigated, would have thrown great light on the main research. As an instance, may be mentioned his omitting to examine the relation of gases to water.

This

relation, of which he had indistinct glimpses, was a source of perpetual embarrassment to him, and led him to imagine changes in the intimate constitution of gases, which were in fact due to nothing more than an interchange of place between the gas in the water and that above the water, or between the former and the external atmosphere. Thus he erroneously supposed that hydrogen gas was transmuted into azotic gas, by remaining long confined by the water of a pneumatic cistern. The same eager direction of his mind to a single object, caused him also to overlook several new substances, which he must necessarily have obtained, and which, by a more watchful care, he might have secured and identified. At a very early period of his inquiries, (viz. before November 1771), he was in possession of oxygen gas from saltpetre, and had remarked its striking ef fect on the flame of a candle; but he pursued the subject no farther until August 1774, when he again procured the same kind of gas from the red oxide of mercury, and, in a less pure state, from red lead. Placed thus a second time within his grasp, he did not omit to make prize of this, his greatest, discovery. He must, also, have obtained chlorine by the solution of manganese in spirit of salt; but it escaped his notice, because, being received over mercury, the gas was instantly absorbed*. If he had employed a bladder, as Scheele afterwards did, to collect the produce of the same materials, he could not have failed to anticipate the Swedish philosopher, in a discovery not less important than that of oxygen gas. Carbonic oxide early

*Series in 253

and repeatedly presented itself to his observation, wit being aware of its true distinctions from other kinds of mable air; and it was reserved for Mr Cruickshank of W to unfold its real nature and characters. It is remarkal that in various parts of his works, Dr Priestley has stat that might have given him a hint of the law, since unfo the sagacity of M. Gay-Lussac, "that gaseous substanc bine in definite volumes."

31 measure of fixed air unites with 1 measure of alkal bolomeasure of sulphurous acid with 2 measures of do. it1 measure of fluor acid with 2 measures of do.

1 measures of oxygen gas with 2 measures nitrous quado nearly; of mill bo

and that by the decomposition of 1 vol. of ammonia, 3 hydrogen are evolved. To squadr

Let not, however, failures such as these to reap all th within his compass, derogate more than their due shar the merits of Dr Priestley; for they may be traced to tha ardour of temperament, which, though to a certain de disqualification for close and correct observation, was th and sustaining principle of his zealous devotion to the p of scientific truth. Let it be remembered, that philosoph the loftiest pretensions are chargeable with similar oversigh that even Kepler and Newton overlooked discoveries, up very confines of which they trod, but which they left to glory on the names of less illustrious followers.h 5t of the general correctness of Dr Priestley's experiments but justice to him to speak with decided approbation. In instances, it must be acknowledged, that his results have rectified by subsequent inquirers, chiefly as respects qua and proportions. But of the immense number of new originating with him, it is surprising how very few are at ance with recent and correct observations. Even in thes examples, his errors may be traced to causes connected wit actual condition of science at the time; sometimes to the impure substances, or to the imperfection of his instrume

the Philosophical Character of Dr Priestley.

9

he sought satisfactory evidence, than for the fidelity with which he reported it. In no one instance is he chargeable with misstating, or even with straining or colouring, a fact, to suit an hypothesis. And though this praise may, doubtless, be conceded to the great majority of experimental philosophers, yet Dr Priestley was singularly exempt from that disposition to view phenomena through a coloured medium, which sometimes steals imperceptibly over minds of the greatest general probity. This security he owed to his freedom from all undue attachment to hypotheses, and to the facility with which he was accustomed to frame and abandon them;-a facility resulting not from habit only, but from principle. "Hypotheses" he pronounces, in one place, "to be a cheap commodity ;" in another to be "of no value except as the parents of facts ;" and so far as he was himself concerned, he exhorts his readers "to consider new facts only as discoveries, and to draw conclusions for themselves." The only exception to this general praise is to be found in the pertinacy with which he adhered, to the last, to the Stahlian hypothesis of phlogiston; and in the anxiety which he evinced to reconcile to it new phenomena, which were considered by almost all other philosophers as proofs of its utter unsoundness. But this anxiety, it must be remembered, was chiefly apparent at a period of life, when most men feel a reluctance to change the principle of arrangement, by which they have been long accustomed to class the multifarious particulars of their knowledge.

In all those feelings and habits that connect the purest morals with the highest philosophy (and that there is such a connection no one can doubt), Dr Priestley is entitled to unqualified esteem and admiration. Attached to science by the most generous motives, he pursued it with an entire disregard to his own peculiar interest. He neither sought, nor accepted when offered, any pecuniary aid in his philosophical pursuits, that did not leave him in possession of the most complete independence of thought and of action. Free from all little jealousies of contemporaries or rivals, he earnestly invited other labourers into the field which he was cultivating; gave publicity, in his own volumes, to their experiments; and with true candour, was as ready to record the evidence which contradicted, as that which

confirmed, his own views and results. Every hint had derived from the writings or conversation of others reservedly acknowledged. As the best way of accelera progress of science, he recommended and practised t publication of all discoveries; though quite aware tha own case, more durable fame would often have resulted delayed and more finished performance. "Those pers remarks," are very properly disappointed, who, for the s little more reputation, delay publishing their discove they are anticipated by others."

JonIn perfect consistency with that liberality of temper has been ascribed to Dr Priestley, it may be remarked a he took the most enlarged views of the scope and objects tural Science. In various passages of his works he has en with warm and impressive eloquence, the consideratio flow from the contemplation of those arrangements in tural world, which are not only perfect in themselves, b essential parts of one grand and harmonious design. He ously recommends experimental philosophy as an agreea lief from employments that excite the feelings or overstra attention; and he proposes it to the young, the high-bor the affluent, as a source of pleasure unalloyed with the an and agitations of public life. He regarded the benefits investigations, not merely as issuing in the acquirement o facts, however striking and valuable; nor yet in the ded of general principles, however sound and important; b having a necessary tendency to increase the intellectual and energy of man, and to exalt human nature to the hi dignity of which it is susceptible. The springs of suc quiries he represents as inexhaustible; and the prospects, may be gained by successive advances in knowledge, as in selves "truly sublime and glorious."

o Into our estimate of the intellectual character of an in dual, the extent and the comprehensiveness of his studies always enter as an essential element. Of Dr Priestley it be justly affirmed, that few men have taken a wider range the vast and diversified field of human knowledge. In d

ting through the greater part of his life a large portion of