LL. M. Rutherfurd—Stability of the Collodion film. 481 
aging about thirty-four stars on each plate; also upon many 
plates of the group about 4 Orionis; also upon many plates of 
the group surrounding 41 Bodtis; also of the group surround- 
ing 4 Cassiopea. 
In addition to the measures of the position and distance of 
the members of the several groups mentioned, very many meas- 
ures have been made upon long lines of star images, at inter- 
vals of one second of time from each other, for the purpose of 
determining the angular value of any given portion of the 
plates. Very many measures have been made for the same 
purpose upon selected star pairs, and the results of these meas- 
ures compared with the results of transits of stars over dia- 
mond lines drawn upon a plate of glass placed in the photo- 
graphic plate-holder at the photographie focus,—and finally 
many measures have been made upon star groups taken on the 
preceding, central and following regions of the plates for the 
purpose of detecting the character and amount of the distor- 
tion, if any, of the images. 
The results of all these measures were so concordant as to 
plates and upon one not albumenized respectively, a shrinkage 
to the following fractions of the whole space measured: in No. 
1, sis, No. 2, g}z, No. 8, ya's, No. 4 ar's3- \ 
were measures of the same plate, but in directions perpendicu- 
_ lar to each other. No. 4 was on a plate not albumenized: 
xpe- 
n for 
examination, and for that purpose the following measures were 
made upon plates, albumenized before the application of the 
collodion, first when leaving the camera and quite wet, and sec-: 
ond when they had become dry; some of the plates were neg- 
