512 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
of the capsule is a thick piece of metal, having a central depression. In 
this depression the lower end of the needle seen in fig. 45 rests, and 
the upper end of the said needle enters a short distance into the socket 
end of the screw P. Communication is thus established between the 
capsule inside and the valve outside. 
A is the inlet for gas. C the outlet to burner. B D a lever pivoted 
Fig. 44. 
to standards at G, and acted upon by the capsule through the needle 
which enters the socket below the screw P. The construction ot the acting 
portion of this valve is such that, whenever the end B of the lever B D 
presses on the disc below the end B, the main supply of gas is entirely 
cut off. At such times, however, a very small portion of gas passes from 
A to C, through an aperture inside the valve, the size of which aperture 
can be adjusted by the screw-needle S, hence the gas flame, which burns 
in a little lantern below the incubator, is never extinguished. 
Changes in atmospheric pressure, however, tend to make the tem- 
perature fluctuate about a degree (Fahr.) on either side of the normal. 
To compensate for these variations, a sliding weight runs on the lever- 
rod D. But this weight serves a yet more important function. It gives 
the opportunity of retarding within certain limits the boiling point of 
