132 Remarks upon Mr. Daniell's Experiments [Feb. 



proves, in the most satisfactory manner, by the elegant process 

 of counting the balls in the two piles, that different quantities of 

 matter may be contained under the same superficies; but the 

 conclusion which he draws from it, that the specific gravities must 

 therefore differ, so far from following as a necessary consequence, 

 is in direct contradiction to every authority that we possess on 

 the subject. It had always been assumed as a fundamental 

 principle, that specific gravity has no connexion with the exter- 

 nal form of a body ; but that it entirely refers to the weight of 

 the substance in question, compared with that of a body of an 

 equal bulk, assumed as a standard of comparison. The following 

 is the definition which is given of it by the celebrated Cotes : 

 " Bodies are said to be specifically, or in specie, heavier or 

 lighter one than another ; when, being equal as to magnitude, 

 the weight of one does exceed or fall short of the weight of the 

 other." * This principle, which, as far as I know, has been 

 universally acquiesced in by all mathematicians and philosophers, 

 must, however, in consequence of the curious discovery of Mr. 

 Daniell, be abandoned. 



A second very remarkable fact, which we learn from these 

 experiments, a fact equally at variance with the generally received 

 opinions, is, that the different parts of homogeneous substances 

 may possess different specific gravities. This newly established 

 principle must necessarily introduce a new method of experi- 

 menting on this subject, and will, indeed, render our former 

 experiments of little value. Provided the substance upon which 

 we operated was homogeneous, and free from impurities, it was 

 never suspected that, its specific gravity could be influenced by 

 its relative situation in the mass from which it was derived. But 

 we now find that this is the case, from this " very unexpected " 

 result of Mr. Daniell's experiments. Hence all our accounts of 

 specific gravities must be corrected, or rather ascertained, upon 

 a new principle ; we must not rest satisfied, as all chemists and 

 mineralogists have hitherto been, with merely operating upon a 

 certain portion of the substance in question ; but we must know 

 exactly what is its shape ; whether it was broken off from a 

 larger mass, and whether it formed the central part of that mass, 

 or was merely one of the " corners," and, indeed, it will be 

 necessary that each of these parts be examined separately. This 

 will, no doubt, be a work of great time and labour ; but we 

 trust that the ingenious gentleman, who has made this curious 

 discovery, will not decline to undertake a task for which he is 

 so eminently qualified. 



A third principle, which seems irresistibly to follow from Mr. 

 Daniell's experiments, is, that the same substance may have its 

 specific gravity c/ianged according to the volition of the operator. 

 When, he is preparing his crystal for the experiment, he may 



* Lectures, p. 51, 



