Chemical and Physical Notes 91 



found the simple air thermometer very good for indicating 

 and measuring quick variations of temperature. It has the 

 advantage of lightness and cheapness. The form which I use 

 is a glass bulb, of about 3 cm. diameter on a straight stem 

 of about 10 cm. length. This can be attached to a U-tube 

 of greater or less diameter, according as the differences of 

 temperature to be observed are great or small. The U-tube 

 has some coloured water as indicator, and the indications of 

 the instrument are compared with those of a thermometer. 

 As the instrument is only put together when it is wanted, 

 the variations of barometric pressure do not affect it. It has 

 the great advantage that it can be connected with a tambour, 

 and thus be made to record. The sensitiveness of the glass 

 air thermometer is about the same as that of a very fine 

 mercurial thermometer made for me by Messrs Hicks. The 

 air thermometer, however, would be more sensitive if the ball 

 were made of thin metal instead of glass. 



Air thermometers of this simple kind described are very 

 easily made so as to give calorimetrical results. It is only 

 necessary to weigh and measure the piece of glass tube before 

 and after blowing the bulb. The shortening of the straight 

 part of the tube after blowing gives the length of it which has 

 been expanded into a ball, and from the known length and 

 weight of the original piece of tube the weight of the bulb is 

 found. By carefully gauging the diameter of the ball its 

 surface can be obtained, and from that the thickness of the 

 glass. When the specific heat of the glass is known, the 

 water value of the bulb is given ; if the air contained is taken 

 into account, the value is increased by from I to 2 per cent. 

 The surface of the ball divided by the water value gives an 

 expression for the sensitiveness of the instrument. 



In Table XV the particulars of several air thermometers 

 are given. As they are made of lead glass, both the density 

 and the capacity for heat per unit of weight are higher than 

 in the case of ordinary German glass, but the specific heat per 

 unit of volume is probably very little affected. 



Calorimetric Constants of Deep-sea Thermometers. It is 

 evident that a knowledge of the calorimetric constants of the 



