.s/A' M'll.LIA.M .S7/:.1//-..\'.V, /.A'..s. 267 



resistance at a temperature of (!(5 Fahr. To allow tin- resistance 

 mil to In- readily afleoted by changt-s m the temperature of the 

 water, it was coiled on a brass tube with both ends OJM-M, allowing 

 a free passage to the water. Sir "VV. Thomson's marine galvano- 

 meter with a mirror and scale was employed to determine the 

 balane-- of the bridge. 



Mr. J. E. Hilgard, assistant in charge of the United States 

 Coast and Geodetic Survey, has sent me the following results of 

 Commander Bartlett's experiments. 



The apparatus was set up on board the "Blake," at Providence, 

 in April, 1881, but owing to there being no ice machine on 

 board, only preliminary experiments were made until the follow- 

 ing August. 



The " Blake " sailed from Charleston on August 4th, running a 

 line over known depths in the current of the (J ulf Stream. A 60 Ib. 

 sinker used in sounding was attached to the end of the cable near 

 the resistance coil, which was allowed to hang freely below. "When 

 well in the strength of the stream a series of temperatures were 

 taken by the Miller-Casella thermometers on the sounding wire, 

 and immediately after the insulated cable was lowered to the sur- 

 face, and water from the surface placed around the comparison coil 

 on deck. The temperature of the attached thermometer read the 

 same as that determined for the surface by the thermometer 

 attached to the hydrometer case. 



Under these conditions the pencil of light from the mirror was 

 on the zero of the scale. During the experiments the vessel was 

 rolling from 10 to lo, and there was a moderate breeze from 

 south-east. The resistance coil was lowered to five fathoms below 

 the surface, and was allowed to remain five minutes ; the circuit 

 being closed, the pencil of light remained at zero. Lowering* 

 were then made to 10, 20, and 30 fathoms, and in each case five 

 minutes were allowed for the resistance coil to assume the tempera- 

 ture of the water, and after adjusting the temperature of the water 

 around the comparison coil, it was allowed to stand five minutes 

 before the final reading was taken. 



The rolling of the vessel affected the mirror so as to throw the 

 light about 5 on each side of the zero point when the circuit was 

 open, and nearly the same when closed ; but as the deflection was 

 the same on either side it was easy to determine the middle point. 



