238 DR. A. MATTHIESSEN ON THE EXPANSION 



together with the temperatures of the thermometers, the one (T) in the box, that (Tj) 

 reaching halfway up the expofsed column, and the one in the balance-case. These 

 thermometers were connected as already described in Part I. The thermometer (T) 

 in the box was read off at a distance by a second observer through a telescope. All 

 these data being noted down, a second and third weighing was made, and as the tempe- 

 rature only altered one- or two-tenths of a degree during the time, it was easily seen 

 whether the weighings agreed with each other; and if this were not the case, fresh 

 weighings were made, and often when these again did not agree, it was found that a 

 small particle ofdust had attached itself to the Avire in the water; in fact this occurs very 

 often, so that, after the weighings are finished, great care was taken to see whether any 

 dust was hanging to the fine wire. Having finished the observations at the one tempe- 

 rature, the cylinder was taken out of the box, the water brought to boil, and kept 

 boiling again for half an hour, and in the same manner as before, the weighings, t&c. 

 repeated, and so on for each difiierent temperature. 



The balance was carefully adjusted, so that 50 grms. in each pan might be changed 

 without showing the slightest difierence in weight. The weights were from time to 

 time compared with each ; the 50 grms. being correct according to the Kew Standard, 

 any alteration found in the smaller weights was allowed for. At least once a day, and 

 with some experiments after each observation, the barometer and thermometer placed 

 by its side were read ofi" for the reduction of weights to vacuum. 



The dipping in and out of the w^ater the fine platinum wu-e did not influence the 

 weighings at all ; wires of somewhat larger diameter could not be used, as with these 

 appreciable difierences were observed. As the weight of a metre of the fine platinum 

 wire was only 0-06 grm., the error caused by the wire dipping in the water may be 

 neglected, it being so small, as only 60 to 70 millimeters dipt in the water (forming the 

 slip-knot, Sec). These weigh about 0*004 grm., and they Avould lose in water 0-0002 

 grm. ; but as we only have to deal with the diflferences of loss of weight in water at 

 different temperatures, these 0-0002 grm. will alter in volume between 0° and 100° to such 

 an unmeasurable extent that they need not enter into the calculations. The column of 

 mercury in the thermometer (T) not immersed in the water was corrected for as described 

 in Part I. 



III. On the Bedetermination of the Coefficients of Expansion of Water. 



To determine the coefficients of the expansion of water, the pieces of glass cut from 

 the ends of the rods and ground to the shape^of a double wedge were weighed in water 

 at different temperatures. The pieces were highly polished, and at one end notches 

 were ground in to give a hold to the platinum wire. 



Between each of the observations at different temperatures the water in the cylinder 

 was reboiled to drive out any air which might have been absorbed during the time of 

 weighing. The water employed was distilled from a copper still (tinned inside), the 

 steam being condensed in a tin worm, and kept for use in a large glass bottle. 



