. On the Potvefs of the frifmafic Colours, &c. 31'i 

 cially fcmi-flLiid or enlirely fluid, as it is found in living ani- 

 mals, can receive an electric charge in the manner of infu-' 

 lating plateS;^ and retain it: befides, we do ftot find that 

 the pellicles and humours of the organ of the torpedo are 

 greafy or oily. This organ therefore, compofed entirely of con- 

 ducing fubfrances, cannot be compared either to the elec- 

 ?rophore or condenfer, or to the Leyden fiaflc, or any ma- 

 ehitie excitable by friction or by any othef means capable 

 of electrify ii^ infulating bodies, which before niy difcoveric* 

 were always believed to be the only ones originallv elcdric. 



To what eie8.ricity then, or to what inftrument ought the 

 organ of the torpedo or electric eeJ, &c. to be compared ? To 

 fhat which I have conftrutled according ta the new prin^ 

 cip'e of ele£lricity, difcovered by me fome years ago, and 

 which my fuceeffive experiments, particularly thofe with 

 which I am at prefent engaged, have fo well confirmed, vk. 

 that condudors are alfo, ill certain eafes, exciters of eleilri- 

 city in the cafe of the mutual contaA of thofe of different 

 kinds, <ScC. in that apparatus which I have named the arii- 

 ficial ehar'tc organ, and which being at bottom the fame 

 as the natural organ of the torpedo, refemWes it alfo in its 

 form, as I have advanced. 



II. InveJligatioH of the Fo^u/ers of (he Pr'ifmatlc Colaurs /» 

 Heat and Illuminate Oljeds ; with Unnarks that prove tht 

 different Rcfrayigibilify of Radiant Heat : fa which is added^ 

 an Inquiry imo the Method of viewing the San advanta- 

 geoujly, with Telefcopes of large Apertures and high Mag-' 

 rtifying Pozuers. Bj William Herschel, LL.D. 

 F.R.S.* 



It is fometimes of great ufe in natural philofophy to doubS 

 of things that are commonly taken for granted ; efpecially as 

 the means of rcfolving any doubt, when once it is enter- 

 tained, are often within our reach. We may therefore fay 

 ihat any experiment which leads us to inveftigate the truth 

 ' From I'ranfiiiliuns bf ihi- Rq^al Socielji of Lotickt jor j.8oo. 



oF 



