682 
PEOFESSOR J. N. LOCKYER ON THE PHOTOGRAPHIC 
pencraliim. When held in this way the ratchet is lifted out of the teeth, and the 
driving clock itself is not affected. 
In order that this form of control may be effective, it is essential that the clock 
should be going too quickly, as it is only capable of retarding the driving rod. 
The controlling pendulum is, of course, regulated to the rate required for the 
particular star which is being photographed. 
Electi'ical control for 10-incli equatorial. 
In Mr. PtUSSELL’s form of control the two parts of the driving rod are connected by 
friction plates. It was found, however, on testing tills arrangement, that when the 
upper portion was held by the electro-magnet the rate of the governors was seriously 
retarded. I therefore asked Messrs. Hammebsley (who carried out the necessary 
alterations of the driving clock), to provide some more efficient substitute, and the 
ratchet wheel was the result. 
(2.) The 30-tnoh Eeflector. 
Instrument E .—Before the erection of the 3-foot reffector, the arraimements at 
Kensington did not provide for the use of a very large aperture, and I was led to 
erect a 30-inch reflector at Westgate-on-Sea, having received grants in aid fi’om the 
Government Grant Fund. The mirror, which is a very fine one of 11 feet 3 inches 
focus, was figured and presented to me by my friend Dr. Common ; for the flat 
(7 inches in diameter) I am indebted to other friends, the Brothers Henry, and I am 
anxious to take this opportunity of expressing my great obligations to them for this 
magnificent help in my work. 
