Manchester Memoirs, Vol. lix. (191 5), No. V& 39 



Sheet 75. 



(22" x 1 7 J".) Kepler's 2nd Law. Dalton's statement 

 of the law is: — "If several bodies revolve around a 

 common centre of force, and if the squares of the Periodic 

 Times are as the cubes of the distance, then the central 

 attraction decreases as the square of the distance in- 

 creases." The diagram refers to the cases of the Earth 

 and Mars, which have relative distances of 2 and 3^ , and 

 periodic times of 1 and 2 respectively, hence 



2 3 I 



— 7-., should be equal to — 



3^" 4 2 2 



and this is found to be approximately the case. 



Sheet 76 



(17" X 2 1 J") Shows that the orbits of the planets 

 are ellipses, the sun being in one focus. 



Sheets 77 and 78 



(21" x 17".) The first explains the production of 

 shadows by a body in the path of the sun's rays. The 

 second one explains lunar and solar eclipses. 



Sheet 79. 



(21" x I7j".) Explains the transit of Venus. 

 From Dalton's notes : — 



" 1639. Horrox of Toxteth predicted the transit of 

 Venus — communicated it to Crabtree of Broughton. 

 They both saw it, the first time that ever was seen — this 

 extra, youth died in the 22nd year of his age." 



Sheet 80. 



A circular diagram, 17" diam. This represents the 

 size of the sun, the relative sizes of the planets are shown 

 within the circle. 



