1904-5.] Form of Bolometer for Physiological Investigation. 827 
A Form of Bolometer adapted for Physiological Investi- 
gation. By Walter Colquhoun, M.A., M.B., Physio- 
logical Laboratory, University of Glasgow. 
(Read May 15, 1905.) 
After a lecture on animal heat towards the end of last session, 
in which I described Langley’s original form of bolometer, with 
its two iron gratings, and mentioned that Dr Stewart, of 
Philadelphia, had referred to the use of tinfoil and leadfoil 
gratings for physiological purposes in his text-book, I started 
to make a bolometer for our department. I should mention that 
some time ago Professor M‘Kendrick, impressed by the probability 
of the bolometer being of use to physiologists, had communicated 
with Professor Langley, who kindly sent him, from Baltimore, 
literature dealing with the subject, and stated that the instrument 
was not made by an instrument-maker. 
The form I adopted for experimental purposes was as figured. 
Into a board were screwed terminals A, B, C, D, E, F, G, which 
are connected by wires as shown. In the gaps D E and F G are 
placed gratings. The galvanometer is placed in the circuit C D'. 
By means of a sliding contact along A B the point D' is found such 
that the galvanometer indicates no current in C D'. If heat be 
now applied to one of the gratings so as to alter its resistance, the 
balance of the bridge is destroyed and the spot of light from the 
