A Map of the World on Flamsteed's Projection. 415 



Whether the platinum plate could have been safely dimi- 

 nished in size to the same extent I do not know : probably 

 not, as the iodine solution was so dilute. 



A striking experiment is to suddenly stop the movement of 

 the plate while the cell is connected to the galvanometer. 

 The needle at once begins to move, falling in less than a 

 minute to about a quarter of its original deflection. On now 

 allowing the plate to start off again, the needle rushes up to 

 its old position. 



These experiments then, though rough, are, I think, suffi- 

 cient to show that we have here a method of comparing 

 measurements of E.M.F. made with open circuit with those 

 made while a considerable current is being drawn from the 

 cell, that the fall in E.M.F. when the plates are stationary 

 is entirely due to the alterations in the strength of the solu- 

 tions next the plates, and that the particular piece of apparatus 

 experimented with deserves the title of a constant voltaic cell. 



LV. A Map of the World on Flamsteed's Projection. 

 By Walter Baily, M.A.* 



[Plate V.] 



IN Flamsteed's Atlas Cmlestis the projection used is one 

 invented by him and described in the Preface to that 

 work as follows : — 



" Conceive the globe or sphere to be compassed about with 

 an infinite number of infinitely fine threads all exactly parallel 

 to the equator. Let all the circles usually drawn upon the 

 globe, as the equator, the ecliptic, the meridians, <fcc, be sup- 

 posed drawn and divided, and let the constellations also be 

 formed upon them, and the stars laid down in their proper 

 places. Let also the meridian passing through the middle of 

 any constellation be conceived drawn on the globe, and covered 

 with a fine thread with as many of the adjacent circles as you 

 may think convenient. Conceive the threads on which the 

 constellation is painted to be cut off from the surface of the 

 globe ; and that which passes through the middle being ex- 

 tended straight on the middle of some paper or perfectly plane 

 superficies, let the rest be placed on it at right angles to the 

 middle meridian, but reverted." 



Flamsteed used his projection only for maps of portions of 

 the celestial sphere, and he did not apply it to the polar 



* Communicated by the Physical Society : read February 27, 1886. 



