S12 



TAfe and Letters of Francis (ialton 



By November 27, 1900, (Jalton had devised a simple small a])paratus 



' This is now in the Gallon Lal)oriit«jry. It consiHts en»ontially of a triple cann-ra; oii' 

 ohjwit is thrown directly on to the f<Myil plane; the other two by aid of two reflecting priKni- 

 are also thrown on to the game plane. The three objects thrown on to the plane arc positive ". 

 negative n and positive 6. Uy throwini; out one or two of the three we can throw on to tin 

 Rcreen (i) positive a, (ii) negative n, (iii) positive 6, (iv) positive a + negative n to show tin 

 uniform grey, (v) negative a + poHitive /), the transformer, or (vi) positive a + the transfomiei 

 giving the darkt-nt^l 6. 



