Professor Leslie on the Coniometer. 385 



Thomson, Regius Professor of Chemistry at Glasgow, whose 

 acLiteness, memory, and extensive reading, are universally ac- 

 knowledged, has, within these very few days, ordered his work- 

 man in Edinburgh to execute for him a copy of the instrument. 

 For myself, I can positively aver, that I never chanced to light 

 on the Memoir of M. Say ; and that, although I have been 

 very diligent, of late years, in collecting philosophical apparatus, 

 I have not found any account of his stereometer in elementary 

 works of science, or met with that instrument in the physical ca- 

 binets I have seen either at home or abroad. I suspect it has 

 been confined to the Polytechnic School, and am yet to learn 

 what sorts of experiments have been made with it. 



While I willingly concede, then, the right of priority, and cor- 

 dially give to the late M. Say the praise of ingenuity and accu- 

 racy of conception, I must consider his stereometer as an imper- 

 fect project, and scarcely applicable, in its original form, to prac- 

 tice. The coniometer possesses several decided advantages over 

 the instrument figured in the Annaks de Chimie : 1st, The part 

 for receiving the powder being long and narrow, the capsule is 

 easily and nicely applied ; but in the stereometer, the recipient 

 is a broad shallow cup, the lid of which, fitting with difficulty, 

 may shut up an undue share of air. ^dl^, The long slender 

 tube is easily pressed down into a wider one, containing mer- 

 cury ; whereas Say's instrument is plunged into an enormous 

 cistern of mercury, or at least a very tall receiver. 2dli/, In the 

 coniometer, the scale engraved on the slender tube marks at 

 once the absolute bulk of the powder or porous substance, 

 or rather the weight of an equal volume of water ; there is a 

 sliding scale on the outer tube, and an adjustment for the varia- 

 tion of the altitude of the barometer. 4>thl^, The slender tube 

 has besides another set of numbers engraved, corresponding to 

 the triplication, as the former does to the duplication, of the vo- 

 lume of included air. By comparing the two results, we are 

 enabled to determine, whether the air contained in the porous 

 substance exists in a condensed state, and to calculate the de- 

 gree of condensation. 5thl2/ and lastly. The coniometer has 

 already indicated some very curious and interesting results, 

 which I regard, however, at present as only approximative. As 

 soon as I have brought the instrument to a more perfect form, 

 I purpose to institute a series of accurate experiments with it. 



