166 Miscellaneous Intelligence, 



T>y the small quantity of air or vapour remaining in the bell-glass, 

 I let the air re-enter gradually ; and on repeating the experiment 

 when the internal air was fifteen or twenty times denser than at 

 the commencement, I found that the repulsion had not sensibly 

 augmented in energy, as should have happened had it been occa- 

 sioned by the motion of the heated air. There were, indeed, cer- 

 tain positions of the mobile disc relative to the fixed one in which 

 the divergence was not so great as in vacuo. 



I tried whether the interposition of an opaque screen, composed 

 of two plates of foil separated by a small interval, intercepted the 

 repulsive action of the fixed disc on the mobile one when either of 

 them were heated ; it appeared to me that the screen prevented 

 repulsion. But does it entirely intercept the action ? is a question 

 difficult to answer in this way ; for the interposition of the screen 

 so that the heat should not be too rapidly communicated to it, in- 

 cludes the necessity of a considerable interval between the fixed 

 and mobile discs. 



In consequence of the directive force which tends to replace the 

 steel wire in the magnetic meridian, the apparatus I have described 

 will serve to measure the calorific repulsion of two bodies at dif- 

 ferent distances. With it also may be made other interesting ex- 

 periments. I should have been desirous that this note presented 

 such results that it might have been more worthy of presentation 

 to the Academy ; but the experiments require time, and are labo- 

 rious, inasmuch as the vacuum has to be re-formed each time the 

 apparatus is changed. I hope that philosophers, more expert, or 

 more at leisure, will not disdain to join in these researches, which 

 promise new and curious results, and may, perhaps, throw light 

 on the theory of the dilatation of bodies by heat. 



P. S. To complete this note I should add my reply to the ob- 

 jection of an illustrious geometer, who inquired if I was certain 

 that the phenomena of repulsion which I had described to the Aca- 

 demy were not due to electricity developed by the heat. In my 

 apparatus the metallic stem of the fixed disc communicated with 

 the earth by the copper tube which passed through the glass plate 

 on which the jar stood ; so that if by throwing the focus of solar 

 rays on to the mobile disc it had been rendered electrical, it would 

 always have been attracted instead of repelled by the fixed disc. 



Neither can we suppose it more probable that the phenomena 

 depend on a magnetic action ; for if by throwing the focus on to the 

 fixed disc it became magnetic, it would certainly have repelled 

 one of the extremities of the steel wire ; but it would have at- 

 tracted the other ; whilst, in fact, it equally repelled the two ge- 

 nerally : a constant repulsion in varied and even opposed circum- 

 stances excludes the supposition of an electric or magnetic action. 



On repeating the above experiments with thicker discs, it did 

 not appear that the repulsive force was sensibly augmented. If 



