Mr Potter on the specific heats of Metals, $c. 75 



truly achromatic and aplanatic construction which will give 

 an oblique pencil as perfect as a centrical one, then will the 

 labours of mathematicians have assumed a proper direction. 

 At present I am afraid they have been hollowing before they 

 are out of the wood. I trust, however, that the time will 

 come when the subject will be taken up in the right point of 

 view, or it will be likely to remain a standing opprobrium ma- 

 thematicorum. 



What could be a more beautiful and original subject for 

 analysis than Mr Lister's discovery of the double aplanatic 

 foci and variable aberration of achromatic object-glasses having 

 their inner curves in contact ? to say nothing of the admirable 

 application of which it is capable. If I was a mathematician, 

 I should feel my honour piqued that it had been made by ex- 

 periment. It is quite plain that compound microscopes and 

 erecting eye-pieces are only part and parcel of the subject of 

 telescopes, and worthy of the same attention. Nothing which 

 concerns the exact sciences can in my opinion be frivolous or 

 unimportant, — a mere subtlety or conundrum haying the charm 

 of exactitude about it must always be respectable, though it 

 may be of no positive utility. 



A great deal has been said about the insignificance of mi- 

 croscopes, and that too much has already been written about 

 them. Such opinions proceed naturally enough from the per- 

 sons who are interested in opposing the new improvements, 

 and are certainly highly worthy of a country where the exact 

 sciences seem to be getting out of fashion, and where the ex- 

 perimental ones take precedence of them. 



Lambeth, April 1, 1831. 



Art. VII. — On the Specific Heats of some of' the Metals, with 

 an exposition of some erro?icous Determinations by MM. 

 Dulong and Petit ; and an examination, as to the Metals, 

 of the important law, that the ultimate particles of simple 

 bodies have all the same capacity for Caloric. By R. Potter, 

 Esq. Junior. Communicated by the Author. 



In the course of my optical inquiries, it became necessary for 

 me to learn the capacities of steel and speculum metal for calo- 



