306 Mr. Daniell's Reply 



dation, and to suggest some experiments, which, to render them 

 beneficial, require much perseverance and extensive co-operation." 

 To those who have done me the honour to read the Essay, I may 

 confidently appeal whether I have not, throughout, maintained that 

 tone of diffidence which the sense of incompleteness required. 



From eighteen months' observations of my own, in this country, 

 compared with twelve months' observations of Captain Sabine, at 

 different intervals, and at different places between the tropics, I 

 thought I saw reason to conclude that the force of [radiation from 

 the sun was greater in the former than in the latter situation. I was 

 aware (and I so expressed myself) that the instruments' made use 

 of were not sufficient to determine the question with any degree of 

 nicety ; but I thought that the irregularities to which they were 

 subject would be in some measure neutralized by the number of 

 the observations. It was from the entire number of observations in 

 this country, compared with the entire number between the 

 tropics, that I conceived myself entitled to argue. Mons. Gay- 

 Lussac has most ingeniously made it appear, that I have drawn 

 a strict comparison with each experiment at each respective 

 place; and he thereupon pleasantly remarks, "Si M. Daniel), 

 pensait que j'accorde une trop grande influence aux circon- 

 stances locales, je lui signalerais une nouvelle decouverte qui 

 decoulerait alors trop directement de ses observations pour qu'il 

 ne fdt pas juste de lui en laisser tout I'honneur : ce serait que le 

 soleil, par des latitudes egales, a une force cchaufFante, plus 

 grande en Amerique qu'en Afrique, et sur le continent que dans 

 les lies." — To Mons. Gay-Lussac be the anticipated honour of this 

 misrepresentation. My argument is this — Captain Sabine (whose 

 rare accuracy in making observations is well known in this coun- 

 try, and is likely ere long to be as well appreciated in France) 

 undertook to measure the force of solar radiation between the 

 tropics, by observing its effects upon a thermometer prepared to 

 receive its greatest impression, placed in the most unexceptionable 

 manner that circumstances would allow, and by comparing them 

 with another screened from its influence, marking as nearly as 

 possible the mean temperature of the air. To accomplish this 



