248 
MEASUREMENT OF HIGH TEMPERATURES. 
[bull. 54. 
water at the outset of the experiment, and is then closed by a pinch 
cock. It is easy to make the current swift enough to keep both the tube 
and the trough at a constant temperature even when the helix I i& 
heated to extreme white heat. 
The helix of the platinum capillary tube is wound in the form of a 
nearly compact spiral and with the internal radius just large enougl] 
to admit the insulator of the thermo-couple. Smaller aud more compacl 
coils are favorable to constant temperature throughout the length of the 
capillary tubes. It is convenient to use two or more such capillary tube 
wound side by side, so as to make what may be called a fasciculated 
helix. The anterior ends of these capillaries are soldered to a sural 
longitudinally perforated brass cylinder h, which is then hermetically 
sealed into the adit tube g h. The posterior ends of the capillaries, which 
like the other ends, return to the trough MM, are bent slightly upward 
so as to discharge the gas into 11 11. As leaks are fatal to the tempera 
Fig. 46. Plan of the capillary apparatus. Scale h. 
ture measurement at J, the platinum tubes must be carefully solderec 
into the vertical wall of the trough M M, through which they pass 
Soldering the tubes in place and sealing them is a difficult operation 
and too much care can not betaken in guarding against clogging of th 
minute capillary canals. Moreover, solder must be kept away from th 
parts of I which are heated. Insufficiently cautious manipulation ii 
this respect rained more than one of my tubes. Unfortunately, the onl; 
satisfactory check on the degree of perfection of the adjustments inadi 
(902) 
