CORRECTION OF MEASURE OF PHOTOGRAPHS FOR DISTORTION. 



(17) 



In the application of these correctio.ns to the measures in Form 21 (see the specimen of that 

 Form) there is a small theoretical doubt, depending on the different focal adjustments of the 

 photoheliograph when used on Ue La Rue's Scale and when used in the Transit. The easiest 

 method of adjusting to focus is by motion of the object-glass ; and in that case (see a short 



3z 



