November 15, 1895.] 



SCmNGE. 



643 



ous device for keeping the tape stretched 

 at a uniforn tension. At intermediate 

 points, 10 meters apart, the tape vs^as sup- 

 ported by insulated v?ire hooks. Paral- 

 lel to the tape, but insulated from it, 

 a German silver wire was suspended in a 

 similar manner except that the tension was 

 not regulated. At the rear end the tape 

 and wire were electrically connected; at 

 the forward end short flexible leads con- 

 nected the tape and wire with the slide wire 

 of the indicator. A third wire trailing along 

 the ground, connected the junction at the 

 rear end with the sliding contact of the in- 

 dicator, having in its circuit the telephone 

 and interrupter. The arrangement was 

 precisely the same as in the ordinary in- 

 strument, the tape and German silver wire 

 acting as the sensitive coils. The connec- 

 tions with the tape were made by adjust- 

 able clamps which could be easily removed 

 when it was time to carry the tape to a 

 new position. The indicator box was con- 

 veniently placed near the forward end of 

 tape, and readings were taken in the ordi- 

 nary manner by holding the telephone to 

 to the ear and setting the hand on the dial 

 to the point of silence. The dial bore two 

 graduations, one showing the temperature 

 of the tape, and the other the linear cor- 

 rection corresponding to the temperature. 

 Thus it was possible, by a single reading 

 taken at the instant when the measurement 

 was to be made, to determine the amount 

 necessary to be added to or subtracted 

 from the length of the tape. 



The experiments at Keeseville consisted 

 of the measurement of a base line 900 

 meters in length and an accurate determ- 

 ination of the coefficient of expansion of 

 the tape. The results showed conclusively 

 that the error from temperature could be 

 reduced to one part in 1,500,000, which was 

 well within the precision of other portions 

 of the work. The coefficient of expansion 

 was determined by two sets of observations, 



the results being 0.00000613 and 0.00000615 

 respectively. 



An interesting set of observations was 

 made on the temperature of the tape at a 

 time when clouds were passsing over the 

 sun. The rapid fluctuations were astonish- 

 ing and indicated that the tape was much 

 more sensitive to temperature changes than 

 a mercurial thermometer. At times when 

 a dark cloud would suddenly obscure the 

 sun the temperature of the tape would drop 

 ten or fifteen degrees in half a minute. A 

 complete account of these experiments will 

 be published in due time. 



The thermophone has also its practical 

 uses, which are as varied as the uses of a 

 thermometer. For use in connection with 

 the ventilation of buildings it possesses 

 qualities which make it more valuable than 

 the ordinary telethermometer. Besides be- 

 ing accurate and comparatively inexpensive 

 it has this further advantage that any num- 

 ber of sensitive coils may be connected to 

 one indicator. Thus in a large schoolhouse 

 a sensitive coil may be located in each room 

 and the leading wires carried to an indica- 

 tor in the janitor's ofiice, where, by using a 

 switch board, the janitor may read from 

 one dial the temperature of any room in 

 the building. 



In buildings it is advisable to dispense 

 with the telephone and current interrupter 

 and use a galvanometer so arranged that 

 the temperature of the distant coil is indi- 

 cated by the deflections of the needle . With 

 such an arrangement it is only necessary 

 to press a button in order to have the needle 

 automatically indicate the tempei-ature. 



In conclusion, it shou.ld be remarked that 

 the thermophone is admirably adapted for 

 obtaining high temperature, i. e., up to 1,500 

 or 2,000° Fahr., and will doubtless find an 

 extensive use in boilers, chimney flues, etc. 

 It "is also the purpose of the inventors to 

 make the instrument self recording. 



Geoege Chandlek Whipple. 



