46 PROCEEDINGS OP THE AMERICAN ACADEMY. 



0.58 mm. iu diameter. The smaller German silver wire was connected 

 with the corresponding copper wire by a thin joint of electrolytically 

 deposited copper. These joints were very satisfactory, but extremely 

 tedious to make. 



In some of our experiments we used fine wire thermal junctions in- 

 serted in shallow grooves accurately cut in the faces of the slabs to be 

 tested. These grooves were made in a Brown and Sharpe Universal 

 Milling Machine by extremely thin hard steel saws (No. 34 B. & S. 

 Gauge) held between flat disks of somewhat smaller diameters than the 

 saws to prevent buckling. The wire that we used fitted the grooves very 

 closely and we hoped that the indications of the thermal couples would 

 enable us to determine the mean temperature of the walls of the groove 

 when the grooved slab was placed against a flat one. We soon found, 

 however, that the results were most irregular, and, although we have 

 s[)eut some time in attempts to make observations obtained in this way 

 trustworthy, we have met with little success. Sometimes our results 

 have been good, and sometimes they have been considerably in error. 

 We do not yet know how to make them always good. It appears that 

 a thermal junction must be pressed firmly against a surface, the tempera- 

 ture of which it is to take approximately. Although we are not ready 

 to discuss this subject exhaustively, we mention our experiences to show 

 why we have abandoned for the present this very obvious manner of 

 inserting thermal junctions into a prism built up out of slabs, in favor 

 of what at first sight seems a less satisfactory device. After some pre- 

 liminary experiments with fine wire thermal junctions laid between the 

 slabs, with and without sheets of tinfoil at the sides of the wire, we 

 determined to use the thin ribbon thermal junctions, elsewhere described, 

 with varnished edges, so that sheets of tinfoil of the same thickness might 

 be laid at the sides of the ribbon, and in this way a sheet of metal be 

 introduced between the slabs. 



It has been necessary for us to calibrate in the course of our work 

 a large number of thermal elements. Some of these when properly 

 protected we have heated with thermometers iu elaborately jacketed air 

 baths or in tanks of water or oil, and some in vapor baths. We have 

 had considerable quantities of nearly pure chloroform, benzol, a^thylen 

 bromide, bromoform, anilin, paratoluidin, naphthalin, chinolin, a naph- 

 thol, acetanilid, naphthylamin, diphenylarain, phenanthren, anthracen, 

 and a few other substances, the boiling points of which divide the ordi- 

 nary thermometric scale below the boiling point of sulphur into small in- 

 tervals. A good number of these, but not all, we have actually used. 



