4:34 A. L. Day and J. K. Clement — Gas Thermometer. 



irregularity as much as possible for the reason given above. 

 Accordingly, another furnace coil was wound with the turns 

 closer together near the openings. This changed the temper- 

 ature gradient considerably without materially improving it 

 (see Furnace II seq. ), after which a third coil was prepared 

 with still closer windings, which proved to be considerably 

 overcompensated and was rejected. In all, we made five sep- 

 arate trials of this kind, in the last two of which (Furnaces III 

 and IV ) a thick-walled iron tube was substituted for the por- 

 celain furnace tube in the hope of gaining increased uniform- 

 ity of temperature through the increased heat conductivity 

 of the tube itself. This arrangement succeeded better, but 

 we found it impossible to so arrange a winding that the 

 temperature opposite the openings was uniform with that 

 at the middle of the tube for all temperatures between and 

 1000°.* A winding which gave good results at the lower 

 temperatures gave insufficient compensation at the higher ones. 

 The obvious possibility of reaching a uniform distribution by 

 subdividing the coil into sections in each of which the current 

 could be independently varied was not tried on account of the 

 cumbersome manipulation required, and in part also because 

 the results which we obtained with considerable differences in 

 the gradient appeared to agree very well among themselves. 



The temperature carried out in the tables in each case repre- 

 sents the integral of the nine pairs of readings described above. 

 The actual error which enters into an observation from the 

 variation in temperature opposite the openings is therefore the 

 error in establishing this integral, which can hardly be greater 

 than 1° C. or "1 per cent. 



It will probably occur to other experimenters, as it did to us, 

 that this difficulty with the exposed ends of the bar is due in 

 part to the unavoidable air currents circulating through the 

 small openings, and that these ought to be checked by the 

 introduction of windows. We made two attempts to reach 

 the difficulty in this way, first using quartz windows set in the 

 opening of the furnace tube itself and therefore heated with 

 the tube ; and second, by the use of glass windows set in the 

 water jacket and therefore outside of the heated zone. The 

 quartz windows behaved very well until high temperatures were 

 reached, when they become displaced by the unequal expan- 

 sions in the apparatus, thereby causing displacements in the 

 apparent position of the lines of the scale. • When the windows 



* A considerable part of the difficulty in correcting the irregular furnace 

 temperature was due to the instability of nickel wire at the higher temper- 

 atures. The oxidation is so rapid that a favorable arrangement of the wind- 

 ings, when obtained, does not give uniform results for more than one or two 

 series of observations. It is our purpose to abandon it in favor of a nickel- 

 chromium alloy or pure platinum. 



