CHEMICAL AND PHYSICAL NOTES. 141 
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 
Taste XVII.—PartiovuLars OF CALoRIMETRIO AIR THERMOMETERS MADE OF 
Leap Guass. 
Number of Instrument. 1. 2 3. 4. 5. 
Original weight of tube (grm.) | 7°724 | 18-508 | 18°4186 | 18-8136 | 18-6169 
» length of tube (mm.) .| 225°7 193°0 192°1 196°0 194°25 
Ditto after blowing . . . .| 197°0 144°0 137°0 126°4 104°0 
Difference 2. . . . . } 28°7 49°0 55°1 70°4 90°25 
Weight of 10 mm. tube (grm.) . | 0°7853 | 0:9590 0°9590 0°9580 0°9580 
Weight of bulb (grm.) . .| 22538 | 46991 | 5-2841 | 6-7443 | 8-6550 
Diameter of bulb(mm.)  . . 24 32 38 45 51 
Volume of ditto(cc.) . . .| 7°238 17°157 28°731 47°713 69° 456 
Surface of bulb (sq.c.m.) . .| 18°095 | 32:170 | 45-364 63°617 81°713 
Volume of glass at sp. gr. = 3.0) 0°7513 | 1-5664 1-7614 2°2481 2°8850 
Thickness of glass(mm.) . .| 0°415 0°487 0°388 0°353 0°353 | 
Water value of bulb, sp. heat 
ome O57 soe we 4. | 074282 | 0°8928 1:0040 1:2814 1°6445 
Surface + water value. . .| 42:26 36°03 45°18 87°25 42°24 
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 1 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 XVII. the particulars of several air thermometers are 
given. As they are made of lead glass, both the density and the 
