56 Light productd by the CoU'tfion of Cane, 



certain general terms to a number of fimilar ideas, or fimilar trains of ideas j confequentljr 

 there cannot well be a new thecwy without a new nomenclature. Till my experiments on 

 heat and light are rendered inconclufire, by numerous contradi(Sory fails, or experiments, I 

 confider myfeif as entitled to ufe my prefent i^omendature for the combinations of light. 



Dr. Bcddoes defires me to inform you, that the Pneumatic Inftitution, fo far as we can yet 

 judge, promifes to do well. We were apprehenfive that prejudice would prevent applications ; 

 but no fooncr was its opening notified to the people, than they began to refort to it. We have 

 already upwards of fifty patients. By degrees we (hall provide apparatus for trying, in every 

 way, fuch gafes or vapours as promife any thing, or ought to be tried. He requefts further, 

 that you would notify that a confiderable error has been difcovered in the copy from which 

 page 381, line 9, of the " Weft-country Contributions" was printed: it fhould be 

 " calomel, three grains," jnftead of " calomel, eight grains." I remain, Sir, with wiflies 

 for the fuccefs of your academical undertaking, 



Yours, with great refpedt, 

 Clifttn^ AprU xub. HUMPHRY DaVT. 



To Mr. Nicholson. 



III. 



Experiments and Obfervatlons on the Silex compofiHg the Epidermis, or external Bari, and eom- 

 tained in ether Parts of certain Vegetables. By HUMPHRY Dap^Y. 



D. 1. A 



FEW days ago, Mr. Coates, of Clifton, informed me that his fon, accidentally 

 rubbing two pieces of bonnet-cane together, in the dark, had perceived a luminous appear- 

 ance. This phenomenon was fufSciently novel and curious to induce me to examine it. 

 I found that all canes of this kind, when brilkly rubbed together, produced fparks of white 

 light. The luminous appearance was much more vivid on coUifion. When the canes were 

 violently ftruck together, fparks nearly as vivid as thofe from the gun-lock were produced. 

 At the fame time a ftrong fmell, fimilar to that generated by the collifion of flinty or the 

 excitement of the ele<5tric fluid, was perceived. 



D. 2. I firft thought that the phenomenon was eleftric, and depended on foroe refinous 

 matter in the cane. The eleftrometer, however, was not fenfibly aft'efted duringthe experi- 

 ment. When the cane was ftruck againft wood of any kind, no light was perceived. 

 When a cane was ftruck violently againft quartz, agate, or any frliceous ftome, the light was 

 as brilliant as when two canes were ftruck together. The Itiminous appearance was pro- 

 duced when {harp fteel was ftruck againft the cane. When the cane was ftruck againft fuJ- 

 phate of ftrontian, or barytes, or carbonate of lime, no light appeared'. 



D. 3. Thefe circumftances induced me to fuppofe that the phenomenon depended on 

 filiceous earth in the epidermis, or in the whole of the cane. To determine this, I took off" 

 a fmall quantity of epidermis from one of the canes. It was hard, white, atul h.id fomethitjg 



the. 



