1903 - 4 .] Mr J. R. Milne on a New Form of Juxtapositor. 363 
spectrophotometer, increased accuracy of measurement would result 
from getting the two bright semi-circles into perfect contact along 
their common diameter. By the^use of this juxtapositor it is 
hoped this may be accomplished, and the accuracy of polari- 
metrical measurements correspondingly improved. 
The experiments which led up to the designing of this form 
of juxtapositor were made in the Physical Laboratory of the 
University of Edinburgh. The apparatus employed was in part 
supplied by a grant from the Moray Endowment Fund, to the 
trustees of which the author’s best thanks are due. 
{Issued separately January 17 , 1905 .) 
