458 MR. A. E. TUTTOX OX THE THERMAL DEFORMATIOX OF THE CRYSTALLISED 
hardness to be obtained with the minimum expenditure of time and trouble. Its cost 
is necessarily very heavy, and the author wishes it to be clearly understood that it is 
not intended as an instrument for ordinary laboratory use, hut as a means of 
obtaining, irrespective of cost, plates blocks or })risms of the highest attainable 
accuracy of orientation and perfection of surface, for the purposes of original investi¬ 
gation. The accompanying illustration represents it. 
The following descrijjtion of the improvements on the instrument previously 
described is appended for the information of other workers, and in response to several 
eiKpiiries which the author has received both from investigators in this country and 
abroad. 
The most important is a new method of mounting the grinding table, which admits 
of its movement in its own plane ; this is introduced in order to he able to vary the 
part used in the grinding more considerably than can be achieved merely by use of 
