TRANSACTIONS OF SECTION A. 549 



Ijarometer is also read at the closing and at the opening of the l liermometer, and 

 the temperature of the water used is noted. Also the observed barometric pressure 

 &t opening is corrected for vapour pressure when water is used, care being taken 

 to ensure, as far as may be done, that the air left in the thermometer is saturated 

 with moisture, though the experiment is carried through with tolerable quickness 

 to avoid loss of air by absorption in the water. 



Weighing No. 1 being subtracted from weighing No. 3, the whole volume of the 

 thermometer (which must be corrected for expansion of the glass) is obtained. 

 Weighing No. 2 being subtracted from weighing No. 3, the volume of the air at the 

 high temperature is obtained. From the ratio of these two volumes the tempera- 

 ture is calculated by well-known formulas. For temperatures below redness the 

 thermometers are made of German or somewhat hard English glass ; for higher 

 temperatures, of combustion-tubing. 



A few words will suffice to describe the copper jacket. . It consists of a con- 

 siderable number (eight in the jacket exhibited) of sheet copper cylinders, each 

 having a bottom, put one inside the other. These concentric cylinders fit each other 

 very closely, there being only space for a lapping with a few turns of the thinnest 

 asbestos thread to hold them together and keep an air space of perhaps 3^ of an 

 inch. 



The internal diameter of the innermost cylinder is about an inch. A stopper 

 of woven asbestos closes the open end of the innermost cylinder and supports the 

 air thermometer and the electrodes, of thick copper, to which the platinum wire to 

 be tested is attached by silver soldering. The platinum wire is in the form of a 

 spiral, with the turns well separated, wide enough in diameter to admit the bulb of 

 the air thermometer. A very powerful Fletcher's ' solid flame ' burner gives 

 ample heat to raise the whole copper cylinder and its contents to redness. 



Experiments described have shown that the temperature within the copper 

 cylmder may be kept for any length of time so constant that there is no variation 

 of electric resistance perceptible with exceedingly sensitive electric measuring 

 apparatus. 



Temperatures lower than 300° 0. have generally been determined with the aid of 

 the vapours of liquids of high boiling points. A very convenient series of organic 

 liquids was proposed by Drs. Ramsay and Young two years ago. 



The determination of the electric resistance of the wire was made by the poten- 

 tial method. An electric series is formed, consisting of a single gravity Daniell, the 

 platinum coil to be tested, a known coil of platinoid on the outside of a large tin 

 vessel filled with cold water (which contains a lump of slaked lime to prevent 

 rusting of the tin vessel), and, lastly, a rheostat to regulate the series. The elec- 

 trodes furnished with spring clips of a high resistance (10,000 ohms) galvanometer 

 are clipped on alternately to the standard coil and the platinum wire under test. 



14. On a new Standard Sine-Galvanometer} 

 By Thomas Gray, B.Sc, F.E.S.E. 



The instrument proposed in this paper consists of a tube, the length of which is 

 much greater than its diameter, covered with a single layer of wire, laid on uni- 

 formly all along its length. In the instrument proposed the tube is ten centimetres 

 in diameter and one metre long. The advantages claimed for this arrangement 

 are: the ease with which the constants can be obtained with sufficient accuracy; 

 the great uniformity of the magnetic field produced at the centre of the coil by a 

 current passing through it ; the ease with which the various details of manufacture 

 work out, and hence its comparative cheapness. 



The coil is mounted on a vertical axis, the line of which passes through the 

 centre of the axis of the tube, and turns above a horizontal table, to which is fixed 

 a scale of degrees on which the angular position of the coil can be read. Arrange- 

 ments are described by means of which the angular position of the suspended needle 

 can be observed by means of a small telescope fixed in one end of the tube. 



' Published in full in the Phil. 3Iag. for October 1886. 



