12 



which measure the electrical potential of the air. A shutter suit- 

 ably geared from the clock intercepts for four minutes, every 

 alternate hour, the passage of the light, the gaps marking a time 

 scale on the paper. During the same the quadrants are put 

 to earth and thus discharged. The mirror then reverts to the 

 zero line and commences a new trace. The readings are reduced 

 to absolute measurements by multiplying by the factor of the 

 instrument. 



This electrograph is like the one at Greenwich observatory.- It 

 is the latest and most improved of Sir William Thomson's instru- 

 ments, and is most valuable and useful for accurately measuring 

 potentials, and extremely so for the observation of atmospheric 

 electricity. No instrument is more ingeniously contrived, deli- 

 cately arranged and capable of producing continuous photographic 

 records than this one. Few of these electrographs are in operation. 

 Some of the observatories of Europe are supplied with an old 

 form of the instrument. In ttie observatories of Montsouris and 

 Kew, especially the latter, the instrument has no gauge and no 

 replenisher, and each pair of quadrants is connected with thirty 

 or more cells, and the needle receives its charge direct from the 

 atmosphere. But with the latest improved instrument no such 

 battery is required. Its potential is controlled by delicate arrange- 

 ments, and the needle is charged through the acids in the jar. 

 While parts of this instrument may be found in the different labo- 

 ratories of our institutions, it is thought that the electrograph at 

 Amherst is the only complete one of its kind in this country. 



Arrangements were made with the Signal Office at Washington 

 for furnishing this observatory with the "official forecasts and 

 cold-wave warnings," but the expense of obtaining the telegrams 

 from the office was so great that it was thought proper to wait 

 until funds could be obtained sufficient to place telegraph instru- 

 ments in the observatory, and thus be able to communicate directly 

 with the central office at AVashington. This can be done at an 

 expense of less than two hundred and fifty dollars, for the United 

 States government will pay for all telegraph service. It is there- 

 fore recommended that money be appropriated for this purpose, in 

 order that a complete signal station may be established at the 

 college. 



Respectfully submitted, 



C. D. Warner. 



