548 Prof. H. L. Callendar on Electrical 



Herceus Quartz-Glass Thermometer. — The smallest size of 

 quartz-glass resistance thermometer constructed by Herseus 

 after the experiments of Dr. Haagn has a bulb 25 mm. long 

 and 3 mm. in diameter, and is therefore very similar in 

 dimensions to an ordinary clinical thermometer. The bulb 

 contains a coil of fine platinum wire wound on a rod of 

 quartz-glass, and protected by a very thin tube of quartz- 

 glass fused over it. The bulb is fused on to a larger quartz 

 tube, containing the two leading wires, which are of gold. 

 The resistance of the coil is 25 ohms nearly at 0° C, but, as 

 there are no compensating leads, the resistance cannot be 

 measured very accurately. This type of thermometer is very 

 suitable for insertion in the mouth, but is unsuitable for 

 records of long duration owing to its shape and the risk of 

 breakage. It does not appear to be quite so sensitive as a 

 mercury thermometer of similar dimensions, partly owing to 

 the low conductivity of the central rod of quartz-glass, and 

 partly to the fact that the leads are not compensated. When 

 inserted in a water-bath at 37° C. this thermometer starts 

 very quickly to rise, but takes about a minute in arriving 

 within a tenth of a degree C. of its final reading, and 

 continues to change appreciably for three minutes, possibly 

 owing to slow conduction along the leads, one of which 

 passes through the centre of the coil. When placed under 

 the tongue, after keeping the mouth closed for ten minutes 

 previously, it arrives within a degree of the final temperature 

 in one minute, but takes seven or eight minutes to get within 

 a tenth of a degree. A typical record obtained with this 

 thermometer is given in fig. 3. 



Flat Platinum Tube 1 hermometer. — This is a type of 

 thermometer which I specially designed for calorimetric 

 work, where quickness of action and small mass are im- 

 portant. It is similar to the flat glass bulb thermometer, 

 except that the containing tube is of platinum about 0*05 mm. 

 thick, which permits the thermal capacity of the bulb to be 

 greatly reduced. The coil is wound on a flat plate of very 

 thin mica, and insulated from the flattened platinum tube by 

 thin strips of mica on either side. The lag of this thermo- 

 meter when placed in a water-bath at 37° C. was so much 

 less than that of the galvanometer that it could not be 

 recorded satisfactorily. Owing to its size and shape, it was 

 not very suitable for insertion in the mouth, as it could not 

 be placed in the usual position under the tongue. When 

 placed along the side of the mouth (after closure for ten 

 minutes) between the tongue and the teeth, it arrived within 

 o, 3 of the final temperature in less than a minute, but 



