34 Gee. Daltoris Lectures and Lecture Illustrations. 



figure to a larger size, and has in addition three views of 

 the eye with the pupil contracted, of normal size, and 

 dilated. 



Sheets 53 and 54. 



(8" x io|" and 17" x 2oJ".) These are in illustration 

 of what Dalton has called the " optical principle " used 

 in the " Essays " in connection with the Propositions 

 concerning the Aurora Borealis, where he says " for it is 

 known to every one, that celestial objects, and objects at 

 a distance in the air, as the sun, moon, stars, meteors, etc., 

 all appear at the same distance, though nothing can be 

 more disproportionate than their real distances." 



Acoustics. 

 Sheet 55. 



(22" x 18".) The transverse vibrations of strings 

 showing the production of the fundamental note and 

 harmonics. This is an enlarged drawing of one on a 

 half-sheet of notepaper, found among Dalton's papers, 

 on which he has written " Young's Theory of Harmonic 

 Tones." 



Sheets 56, 57 and 58. 



The first is a small diagram (8" X 13") on which 

 Dalton has carefully drawn seven organ pipes producing 

 fundamental and harmonic tones, and has marked the 

 position of the nodes and anti-nodes. He has also repre- 

 sented the condition of the air of the sound-wave by 

 spirals whose diameter is gradually varied. Three relate 

 to open and three to closed pipes. A pitch-pipe is also 

 shown, which is provided with a piston for altering the 

 length of the tube. No. 57 (i6£" X 1 3") gives the first 

 six cases. No. 58 (27" X 19") includes the pitch-pipe, 

 four closed pipes and three open pipes. 



