38 Gee, Daltoris Lectures and Lecture Illustrations. 



apart with increasing height. This diagram also shows a 

 logarithmic curve. 



Sheet 70. 



(20 ,/ X30 // .) A rough map of Great Britain showing 

 an isogonic line. This is drawn through London, and 

 the declination when read off by a protractor is 20°W. 



Sheet 71. 



(i7' / X2o".) A diagram explaining the theory of the 

 winds. 



Astronomy. 

 Sheet 72. 



(22 // X32 // .) This diagram is repeatedly referred to 



by Dalton in his Lecture Notes on Astronomy. In 



Lecture 8, April 17th, 1820, his rough notes give: — 



" Gravitation explained — Earth, Diagram. 



— Attraction of each particle of matter is inversely as 



the square of the distance. 

 — Force of Gravity at the Earth's surface Max. 

 — Force above, inversely as square of distance from 



centre. 

 — Force below — directly as distance from centre." 



The diagram (22 // X32 // ) represents the earth attract- 

 ing a weight of 1 at the surface of the earth and balances 

 a weight of 4 placed at distance 2 from the centre of the 

 earth. The weights are placed in the pans of a balance 

 having short and long suspensions. The attraction at 

 distance 2 is marked \, and at distance 3, \. 



Sheets 73 and 74. 



(20" x 16" and 22" x 18".) These Dalton used to 

 explain Kepler's 1st Law, which he states as : — "A body 

 revolving round any centre of force describes equal areas 

 in equal times." 



