Dr Brewster on the motions of the Molecules of Bodies. 215 



Watt's rotatory double engines working machines for bruis- 

 ing tin ores at 



Length of 

 crank in feet. 



Huel Vor, 24 6. 8. 12. 16.9 17. 

 27 5. 2.5 12.5 17.3 19.7 

 16.5 5. 2.5 8.5 9.B.Q 13.4 

 Average duty of rotatory double engines, 16.7 millions. 



* Watt's double engine. 



-f The steam is first admitted into a high pressure cylinder, 

 whence it passes into a Watt's single engine, both pistons be- 

 ing connected with the same lever. All the others are Watt's 

 single engines. 



Art. V. — Observations relative to the Motions of the Mole-' 

 cules of Bodies. By David Brewster, LL. D. F. R. SS. 

 London and Edinburgh. 



jNoTwiTHSTANDiNa the great interest which has been every- 

 where excited by the observations of Mr Brown respecting the 

 motions of the Molecules of Bodies, I should not have thought 

 of calling the attention of the Society to the opinions which I 

 entertained, or to the experiment which 1 had accidentally 

 'made in reference to this subject. 



As I am, however, the only surviving member of those who 

 took an active part in the discussion and examination of this 

 matter when it was presented to the consideration of this So- 

 ciety nearly fifteen years ago, I feel it incumbent upon me to 

 call your attention to the facts and views which then came un- 

 der our .notice. 



On the 2d May 1814, Dr Drummond of Belfast communi- 

 cated to tliis Society a paper " On certain appearances ohserv- 



' ed in the dissection of the Eyes of Fishes.'''' Having washed 

 off the silvery part of the choroid coat of the haddock into 



I about half a teaspoonful of water, the water became of a milky 

 colour, owing to innumerable slender, flat, silvery spicula, 

 which composed the substance of the choroid. " They seem- 



