P 
cite, Sea wl ey 
ON DIMORPHOUS BODIES. 163 
_ On the present state of our knowledge in regard to Dimor- 
phous Bodies. By Prof. Jounston. 
Tue subject of the following Report is one in regard to which 
our knowledge is yet in its infancy. It has arrived, however, 
at that state in which a detailed exposition and critical exami- 
nation of all the facts hitherto observed, is likely to lead to new 
inquiries, to call new observers into the field, and thus more 
rapidly to dissipate the obscurity with which it is invested, It 
will not be uninteresting also in after years to look back upon 
the facts actually established, the views entertained, and the 
speculations hazarded at the present time,—to mark how far 
the phenomena were rightly interpreted,—what glimmerings of 
truth were mingled with the early speculations,—at what rate 
this department of knowledge had subsequently advanced, and 
how far this advance had been promoted or retarded by the 
hypothetical views of its first cultivators *. 
Lp 
1. When the forms and dimensions of crystallized bodies 
began to be accurately observed and recorded, it was soon re- 
cognized that these might be classed among the most distinct 
and specific characters which solid bodies possessed. Observa- 
tion seemed at first to show that each substance, simple and 
* How much the progress of science depends on the mode in which pheno- 
mena are interpreted by the first observers is strikingly illustrated in the case 
_ of certain experiments of Robert Boyle. He observed that when copper, lead, 
iron, and tin were heated to redness in the air, a portion of calx was formed, 
and there was a constant and decided increase of weight.—(Experiments to 
make Fire and Flame ponderable, London, 1673.) This experiment he re- 
ted with lead and tin in glass vessels hermetically sealed, and found still an 
increase of weight, but observed further, that when “ the sealed neck of the re- 
tort was broken off, the external air rushed in with a noise.’—(Additional ex- 
periments, No..V., and a discovery of the perviousness of glass to ponderable 
parts of flame, Exp. III.) From this he-reasoned correctly, that in calcination 
the metal lost nothing by drying up, as was generally supposed, or that if it did, 
“by this operation it gained more weight than it lost.” —(Coroll. II,) But 
this increase of weight he attributed to the fixation of heat, stating it as ‘“ plain 
_that igneous particles were trajected through the glass,” and that “ enough of 
them to be manifestly ponderable did permanently adhere.” Had he weighed 
his sealed retort before he broke it open, he must have concluded that the metal 
_had increased in weight at the expense of the inclosed air. He stood in fact 
on the very brink of the pneumatic chemistry of Priestley; he had in his 
hand the key to the great discovery of Lavoisier. How nearly were those 
hilosophers anticipated by a whole century, and the long interregnum of 
Philogiston prevented! On what small oversights do great events in the his- 
tory of science as of nations depend! 
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