154 DR. E. ANGUS SMITH ON A 



PElevation des Vapeurs et des Exhalaisons, demontree 

 mathematiquement/ published at Bordeaux in 1743. This 

 and the next mentioned are written in Latin and French. 



He says : — " IV. I put a vessel of boiling water at a 

 window, so as to have more light. I observed two kinds of 

 watery particles rising from it : the first, of a white colour, 

 dividing into different parts, remained for some seconds on 

 the surface ; and then I saw one division after another sepa- 

 rate from the surface and rise into the air with an accelerated 

 movement. 2. Whilst theVater boiled, the vapour moved 

 about two feet and a half in three seconds. 3. Amongst 

 the vapours I saw another kind — small transparent glo- 

 bules, not hollow — which rose very quickly about a foot 

 high ; but their motion was uniformly retarded, and they 

 described a parabolic curve in descending. 



" V. The principles of mechanics teach us that bodies 

 which describe a parabolic curve are pushed by a violent 

 force; it follows that the second kind of particles are 

 pushed out of the water and rise by a violent impulsion. 



" VI. Since this class of particles falls back, these cannot 

 be called vapour. 



"VII. Since the little particles keep a spherical form 

 in the midst of the air by reason of the equal adhesion of 

 their parts, the vapours ought also to have a spherical 

 form." 



" X. I exposed a vessel of boiling water to the rays of 

 the sun, which entered by an aperture into a chamber. 

 I placed myself in such a way that my eye made an angle 

 of 42 degrees with the falling ray ; and I was unable to 

 see in the vapours the colours of the rainbow. To be 

 more certain, I caused a jet of water or fine rain to fall 

 into the middle of the vapours ; and having placed myself 

 as was required, I saw two segments of a rainbow in the 

 middle of the vapours— that is to say, a segment of the 

 principal bow and a segment of that of which the colours 



