642 



SCIENCE. 



[N. S. Vol. II. No. 46. 



The operation of taking a reading with 

 the thermophone is as follows: The helix 

 containing the sensitive coils being placed 

 at the point where the temperature is de- 

 sired, and the leading wires being connected 

 to the binding posts of the indicator box, the 

 current is turned on and the telephone held 

 to the ear. A buzzing sound in the tele- 

 phone is found to increase or diminish as 

 the hand is made to approach or recede 

 from a certain section of the dial. By 

 moving it back and forth a position may be 

 found where the telephone is silent. When 

 at this point the hand indicates the temper- 

 ature of the distant coils. The instrument 

 is extremely senitive. An inexperienced 

 observer may easily set it to one-tenth of a 

 degree. With special instruments having 

 a small range it is possible to make read- 

 ings with much greater precision. 



One of the uses to which the thermo- 

 phone was put at the Summer School was 

 that of ascertaining the temperature at 

 various depths and at various places in 

 Lake Champlain. A large number of ob- 

 servations were taken. The accompanying 

 diagram. Fig. II., shows the results of two 

 sets of observations taken where the depth 

 was 333 and 896 feet respectively. It will 

 be noticed that below a depth of 50 feet the 

 readings at the two places agreed almost 

 exactly; above that point they differed 

 somewhat, but each curve preserved its reg- 

 ularity. It is interesting to observe how 

 great a change of temperature there was in 

 the iirst 50 feet below the surface, and how 

 slight a change there was near the bottom. 

 At a depth of 100 feet the water was but 3° 

 warmer than at the bottom. 



At the deepest place in the lake, which 

 was found opposite Essex, N. Y., the tem- 

 perature at 370 feet was 39.35° F., a point 

 only slightly above the temperature at 

 which water is densest. Unfortunately the 

 thermophone wires were not long enough 

 to reach to the bottom, which was 396 feet. 



The fact that this temperature so near the 

 point of maximum density was found during 

 the summer season indicates that the water 

 near the bottom is in a continual state of 

 stagnation. It is probable that there is lit- 

 tle circulation below a depth of 200 feet. 



In passing it is interesting to note the 

 growing interest that is being taken in the 

 study of the temperature of lakes in con- 

 nection with that of the micro-organisms in 

 the water. The seasonal occurrence of 

 many of these forms which cause trouble in 

 water supplies has been shown to be directly 

 connected with the vertical circulation of 

 the water. Knowledge of the extent and 

 character of these vertical currents can best 

 be obtained by observing the temperature 

 of the water at different depths. 



One of the most interesting of the special 

 uses of the thermophone principle is in 

 connection with the accurate measurement 

 of distances by means of a steel tape. 

 Heretofore the greatest objection to the use 

 of a steel stape for the measurement of a 

 base line has been the alterations in its 

 length due to varying temperature and the 

 impossibility of correctly ascertaining its 

 temperature at the moment of use. Ther- 

 mometer readings taken alongside the tape, 

 or even with the bulb in contact with 

 it, cannot give its exact temperature. 

 Especially is this true when the work is done 

 in the daytime and with the sun shining. 

 For this reason the most accurate work has 

 usually been done at night when the temper- 

 ature of the tape is siabstantially the same as 

 that of the air. By the application of the 

 thermophone principle the tape itself may 

 be used as a thermometer and its exact tem- 

 perature easily determined. This was ex- 

 perimentally demonstrated at the summer 

 school at Keeseville, where the apparatus 

 was used for the first time. 



The steel tape, 100 meters in length, was 

 suspended a few feet above the ground be- 

 tween two iron poles which bore an ingeni- 



