THE NOBLE SCIENCE. 241 



fastened large squares of glass, like the panes of win- 

 dows, placing them in such a manner that they should 

 not overshade one another. On the trial, it appeared 

 exactly as Dr. Dufay had apprehended. The lowest 

 surface of the lowest piece of glass was first wetted ; 

 then the upper, then the lower surface of the pane next 

 above it, and so on till all the pieces were wetted to the 

 top. Hence it appeared plain to him^ that the dew 

 consisted of the vapours ascending from the earth during 

 the night-time, which, being condensed by the coldness 

 of the atmosphere, are prevented from being dissipated, 

 as in the day-time, by the sun's heat." 



We are told of other experiments, the result of 

 which " was quite conformable to his expectations." 



On the other hand, we find that " M. Muschenbrock, 

 who embraced the contrary opinion, thought he had in- 

 validated all Dr. Dufay's proofs, by repeating his expe- 

 riments, with the same success, on a plane covered with 

 sheet lead. But to this Dr. Dufay replied, that there 

 was no occasion for supposing the vapour to rise through 

 the lead, nor from that very spot ; but that, as it arose 

 from the adjoining open gTound, the continual fluctu- 

 ation of the air could not but spread it abroad, and 

 carry it thither in its ascent." 



" Who shall decide, when doctors disagree?" 



From the combination of all circumstances, which it 



