RECORDS 5 



and bottom measured. The deflections obtained were of the 

 same order of magnitude as those produced by the earth's field. 

 The deflections thus obtained giv^e evidence of magnetic forces 

 of sufficient magnitude to explain the deviations observed in the 

 plumb-lines in the Tamarack shaft. 



Professor Hallock also described a form of recording ther- 

 mometer which he had lately devised. It consists of a large cop- 

 per bulb connected by means of capillary copper tubing to a 

 series of cells similar to those used in the construction of aneroid 

 barometers. The bulb, tube and cells were filled with oil and 

 the recording mechanism attached to the aneroid cells. 



Mr. H. C. Parker gave the results of some experiments he 

 had made on the variation of contact resistance with change of 

 electromotive force. The resistance used in the experiments 

 consisted of oxide of manganese on cobalt glass, the new form 

 of standard high resistance described in a previous paper given 

 before the academy. The electromotive force employed con- 

 sisted of TO, 50, and 100 diy cells, respectively. It was found 

 in every case that the resistance decreased with increase of elec- 

 tromotive force. This decrease might be only a small per cent. 

 or the resistance might be reduced to a small fraction of the 

 original value. Improving the contacts rendered this change 

 in resistance much less marked. It was suggested that this 

 decrease in resistance when the electromotive force was increased 

 might be due to a kind of coherer action taking place at the con- 

 tacts. Very high resistances measured by the electrometer 

 method were found practically to obey Ohm's law. It was 

 pointed out that in such cases the contact resistance was prob- 

 ably only a small portion of the entire resistance. 



Section adjourned. 



F. L. Tufts, 



Secretary. 

 SECTION OF BIOLOGY. 



January 13, 1902. 



Section met at 8.15 P. M., Professor C. L. Bristol presiding. 

 The minutes of the last meeting of Section were read and 

 approved. 



