726 ANNUAL EEPOET SMITHSONIAN INSTITUTION, 1912. 



are frequently useful. By my arrangement it is possible to switch 

 from one wire to another very quickly. The 1° scale is essential in 

 very cold water, but for warmer water the coarser scale is necessary. 



The thermometer may be connected so as to read the temperature 

 directly, in which case the resistance of the bulb is compensated by a 

 known resistance box. In tliis way the value of the resistance 

 from previous cahbration gives a measure of the temperature. 

 The thermometer bulb may also be connected differentially with a 

 second equal bulb, and only differences in temperature recorded on 

 the chart. This method can be apphed to give the difference in 

 temperature between the bow and the stern of a ship. Thus a 

 ship so equipped could not possibly run into ice as long as the bow 

 thermometer was equal to the stern thermometer. 



In order to measure the temperature of the river or sea water 

 the thermometer bulb can be trailed by guy ropes alongside, and 

 the lead cable carried through heavy copper pipes up to the deck 

 of the ship. From there the cable can be carried to the chart- 

 house or other convenient location. The thermometer bulb may 

 also be placed in a tank fed from the circulating water in the engine 

 room. Tliis method is desirable on a fast moving ship or in regions 

 where much floating ice is about. 



It will be seen that the microthermometer is a refined electrical- 

 resistance thermometer. 



PRACTICAL TESTS OF THE MICROTHERMOMETER. 



Reahzing the great menace to navigation in the presence of ice, 

 I was anxious to find whether refined measurements of the tempera- 

 ture of the sea could be used to warn a ship at night or in time 

 of fog. 



As a preliminary test of the sensitiveness of the instrument, I 

 had some experiments made in the St. Lawrence River during the 

 time of the ice-breaking work. The C'. G. S. Lady Grey, having 

 cleared out the ice from the channel as far as Lake St. Peter from 

 Quebec, was detailed to steam slowly up the river toward the 

 unbroken ice sheet in the lake. The edge of the ice was sharp 

 and weU defined, and extended out from the shore along the banks of 

 the river. The current of the river flowed from under the ice in a 

 sUghtly diagonal direction, so that, steaming in the open water, the 

 current flowed in such a way as to pass under the edge of the shore 

 ice. The ship started 2 miles below the upper edge of the ice, and 

 measurements of temperature were taken at intervals up to the ice. 

 Figure 3 shows the character of the temperature curve obtained, 

 and illustrates how accurately the microthermometer registers even 

 so smaU a termperature change as one-tenth of a degi-ee per mile. 



