Mr. Kirby and Mr. MacLeay oti the Tarsi of Insects. 267 



position of the silicates by formulae, it would certainly be more 

 simple to consider silica as formed of an atom of silicium and 

 an atom of oxygen ; but it then would be difficult to conceive 

 the existence of the silicates which contain six times the oxy- 

 gen of the base, as in the apophyllite, — in which an atom of 

 potash would then be combined with 1 2 atoms of silica. 



To conclude : It still remains to be decided to what class of 

 simple bodies silicium belongs. Since it has no lustre, nor 

 the property of conducting electricity in the state in which it 

 has hitherto been obtained, it is evident that it cannot be 

 classed among the metals, and that its properties bring it near 

 to boron and carbon. Some systematical philosophers will 

 in consequence, doubtless, give it the name of silicori, to indi- 

 cate by its termination the class of combustibles to which it 

 should be referred. But I look upon this denomination as use- 

 less ; for thei'e is not any true limit between the metals and 

 the metalloids. Carbon possesses the metallic lustre, and 

 conducts electricity, but it is not considered as a metal ; and 

 if silicium could be melted, it then perhaps would have these 

 properties, which it does not possess in a pulverulent state. 

 Uranium, under this last form, can be distinguished but with 

 difficulty by its appearance from silicium ; and when crystal- 

 lized, on the contrary, it has the metallic lustre and is trans- 

 parent on the thinnest edges. Columbium and titanium also 

 approach silicium by their chemical properties ; and would it 

 not be well to separate them from the metals, in order to unite 

 them to the metalloids, — that is to say, to the non-metallic com- 

 bustible bodies ? I only wish to show, by these remarks, that 

 there is no natural limit between these bodies ; and that when 

 their electric relation only is considered as exact, it is quite 

 indifferent whether we place a combustible body among the 

 metals or not. — {Annalai der Physik und Chemie.) 



XLIII. A Letter from the Rev. W. Kirby in explanation of 

 his Remarks upon the Notice, given in the Philosophical Ma- 

 gazine, of Mr. W. S. MacLeay's Paper on the Tarsi of cer- 

 tain Insects. 



To the Editor of the Philosophical Magazine and Journal. 



Dear sir, Wel>b's Hotel, Piccadilly, April 14, 1825. 



¥T gives me j^rcat pain and concern to learn that some gen- 

 ■^ tlemen have regarded my remarks upon your statement of 

 the ol)ject of Mr.W. S. MacLeay's paper "On the Structure of 

 the Tarsus in theTetranierousandTrimerousCeleopteraof the 

 French Entomologists," in a Hglit very different from what \ 

 intended, and as having the air of an attack upon him. I 



L 1 2 hasten 



