344 
MR. C. CHREE ON THE EFFECTS OF PRESSURE 
diameter of a cross section, by means of which a considerable couple could be exerted. 
The pressure was applied to the cobalt by means of a sort of ram-rod rigidly attached 
to the inside of the brass cap. When the cap was screwed on this ram-rod advanced 
into the brass tube, and came to bear on the end of the cobalt rod. 
Drawing of the brass tube containing the cobalt rod, removed from the coil. 
A Closed end of brass tube. 
B Pin which can be slipped through the holes in the cheeks attached to one face of the coil and, as in 
the figure, through the diametral hole bored in the solid end of the brass tube. 
C Screw cut on the outside of the brass tube at its open end. 
D Brass cap with sci’cw cut on its inside answering to C, and carrying ram-rod arrangement for 
applying pressure to the cobalt rod. 
EE Projectin g arm, by means of which the cap is screwed on. 
In the original experiments, conducted in August, 1888, tbe brass tube was firmly 
imbedded in a block of wood, fixed inside a magnetising coil. This coil had a length 
of 19‘8 cms., and consisted of five layers of very thick copper wire. A current of 
one ampere produced a field varying from 9'26 C.G.S. units at the centre of the rod 
to 6‘85 units at its ends. This, it must be admitted, is not a very uniform field, but 
the fall occurred mainly within a centimetre or two of the ends of the rod. 
In this preliminary investigation the observations were taken somewnat roughly. 
The reason they are referred to here is that they clearly showed the existence of a 
cyclic and a non-cyclic effect of pressure, and also the existence of a Villari point for 
the former effect. Further, the result of experiments on several different occasions 
agreed in giving 120 C.G.S. units as a close approximation to the strength of the 
field due to the current at the centre of the rod when the Villari point appeared. 
The mode of variation of the several effects with the strength of the field showed also 
a general agreement with the subsequent more accurate observations taken with a 
different coil. This seems to warrant the belief that the phenomena observed do not 
owe any of their essential features to peculiarities of the apparatus. 
When it was attempted to obtain accurate results with the original apparatus 
various difficulties were encountered. In overcoming these I am much indebted to 
the ingenuity of Mr. Bartlett, the assistant at the Cavendish Laboratory, who 
constructed the new apparatus. 
