880 Royal Medical Society of Edinburgh. 



the plates : at the same time, however, the common elccliical 

 powers were diminished ; for such a pile did not affect an elec- 

 trometer more powerfully than when the cells were filled with 

 pure water, or when paper was interposed between the plates, 

 as in the column of De Luc. 



The effect of increasing the nutnber of alternations was exhi- 

 bited bv tlie large Voltaic apparatus constructed iu the Royal 

 institution by Sir H. Davy. It produced a most brilliant arc of 

 flame when two points of charcoal, connected with its extremes, 

 were brought near each other ; in vacuo tlie discharge was some 

 inches in length, and exliil)ited a star and halo of blue light upon 

 the negative point, and a bright spot and brush of light up«n the 

 positive point: these effects were particularly distinct and beau- 

 tiful. The fusion and combustion of the metals, and the diffe- 

 rent conducting powers of fluids, were also shown by the help of 

 this apparatus. 



The increase in the quantity of electricity by increasing the 

 size of the plates, was illustrated by a battery composed of twenty 

 plates, each being two feet square. The largest apjjaratus of 

 this kind had been constructed by Mr. Children : it consisted of 

 twenty plates, each six feet wide, and two feet eight inches deep. 

 Its powers of igniting metallic wires were of tlie most surprising 

 description ; but as an account of the experiments made by 

 means of it was about to be laid before the Royal Society, Mr. 

 Brande did not minutely describe them. A singular experiment 

 vvao exhibited, hi which a wire of silver and one of the same di- 

 ameter of platina, united end to cud, were made part of the cir- 

 cuit ; the platina wire only became red hot : the effect was re- 

 ferred to the suj^erior conducting power of silver to that of pla- 

 tina, the heating effect being greatest where most resistance is 

 offered to the passage of electricity. 



The Professor exhibited sonic other forms of the Voltaic appa- 

 ratus, and concluded his Lecture with some observations on the 

 relation of electricity to ti\e phaMiomena of lieat, and on its 

 power of producing or passing into ra,diant matter, the more fulf 

 discussion of which would be resumed in his next and concluding 

 hcture. 



ROYAL MEDICAL SOCIEXy, EDINBURGH. 



The Royal Medical Society propose as the subject of their 

 Prize Essay for the year ISIG the following question : 



*' What changes of composition does the process of digestion 

 in quadrupeds produce on earths, oxides, and earthy, alkaline, 

 and metallic salts ?" 



A set of book-^j or a medal of five guineas value^ will be given 



annually 



