M. J. E. Mayer on the Forces of Inorganic Nature. 371 



sliding vertical door containing a hole about %\ inches in dia- 

 meter, which was accurately closed with a disk of coloured glass. 

 In all cases the deposits were furthest from the light — and 

 naturally so, seeing that a coloured object absorbs the heat more 

 readily than a white one, and keeps the side of the bottle nearest 

 to it of a higher temperature than the other parts. 



One more point remains to be noticed. TV hen mercury was 

 exposed to the light in a tall narrow glass, no reliable results 

 were obtained, that is, no deposit was formed that appeared to 

 arise from the condensation of vapour. On two or three occa- 

 sions metallic tears were seen in the vessel, but it was never clear 

 to me that they did not arise from some shaking or disturbanee 

 of the vessel. I could not reproduce even this unsatisfactory 

 result in a narrow vessel, though I carefully tried for it by fur- 

 nishing the vessel with a cap and stopcock and exhausting it 

 with a syringe. I was also further surprised to find that a baro- 

 meter-tube of thick glass charged with camphor and exhausted, 

 produced little or no deposit even on the warmest days, and by 

 exposure to direct sunshine. No sooner, however, had I dis- 

 missed the action of light from this subject, than the whole 

 matter became clear. A thick glass tube by exposure to the 

 light does not cool unequally, but slowly varies in temperature 

 throughout its mass, so that no deposit either of mercury or of 

 camphor is possible. If, however, the tube be thin, of large dia- 

 meter and mounted, so that while one part is exposed to radia- 

 tion the other part is protected, partial cooling is possible, and 

 a deposit is produced. This, too, furnishes an explanation of a 

 fact that had often surprised me. In barometers of large bore 

 there is a deposit of mercury in the Torricellian vacuum on the 

 side nearest the light. I had never seen this in a tube of small 

 bore, though I had frequently looked for it in my own instru- 

 ment. Some of the barometers of large bore in the International 

 Exhibition have very fine deposits of mercury vapour in the Tor- 

 ricellian vacuum, but in such cases they are mounted so that the 

 tube is more or less exposed. Where the tube is boxed in and 

 protected from radiation there is little or no deposit. 



King's College, London, 

 Long Vacation, 1862. 



XL VIII. Remarks on the Forces of Inorganic Nature. 



By J. R. Mayer*. 



THE following pages are designed as an attempt to answer 

 the questions, "What are we to understand by " Forces M ? 



* Translated from the Annate* der Chemie vnd Pharmacie, vol. xlii. 

 p. 233 (May 1842), by G. C. Foster, B.A., Lecturer on Natural Philosophy 



