EARLY LIFE. 69 



rotatory motion of the projectile, and its condensing 

 the air. 



But I recollect an experiment which, accompanied 

 by my brother James and Eeddie, I tried, in order to 

 ascertain the effects of the rotation. It was to fire 

 a bullet from a fowling-piece placed horizontally, 

 through a series of screens placed vertically. It was 

 found that the bullet first deviated to the left, and 

 then, on piercing the first screen, swerved to the right, 

 and so at each screen changed its direction indicat- 

 ing, as we supposed, that the direction of rotation was 

 changed by the screens. 



I, however, soon returned to pure mathematics, 

 and several of the propositions afterwards mentioned 

 in my paper on Porisms, were investigated at this 

 time. I was also diligently employed in experiments 

 upon light and colours, and conceived that I had 

 made some additions to the Newtonian doctrine, 

 which I sent to the Eoyal Society in the summer of 

 1 795. The paper was very courteously received ; but 

 Sir Charles Blagden (the Secretary) desired parts to 

 be left out in the notes or queries as belonging rather 

 to the arts than the sciences. This was very un- 

 fortunate ; because, I having observed the effect of a 

 small hole in the window-shutter of a darkened room, 

 when a view is formed on white paper of the external 

 objects, I had suggested that if that view is formed, 

 not on paper, but on ivory rubbed with nitrate of 

 silver, the picture would become permanent; and I 

 had suggested improvements in drawing, founded 



