412 F. Dellmann on Atmospheric Electricity. 



mensions were unimportant, — the distances, on the contrary, 

 much more so ; and further, that of these distances, the one 

 between the strip and the lower graduated circle was most im- 

 portant, that between the strip and the balance-arm coming 

 next ; the last distance, however, is less important the smaller 

 the distance between the strip and circle; for the distance 

 between the strip and arm being great, the following series of 

 reduced torsions were obtained : — 



1-83, 4-77, 8-39, 13-64, 21-40, 35-03, 5820, 100. 



Genex-al Tables, then, can only be constructed for definite di- 

 stances ; and since no one is likely to be wiUiug to prepare Tables 

 for a number of such possible distances, each experimenter who 

 wishes to use the instrument must reconcile himself to the prepa- 

 ration of his own Tables. One might prescribe certain definite di- 

 stances and furnish Tables for these,but I am convinced thatevery 

 one will prefer to construct his own Tables, since the necessary 

 preliminary experiments are no longer onerous, and the calcula- 

 tion can be made in a couple of hours. I also possess different 

 Tables for the two instruments at present in use, and they differ 

 considerably as well from each other as from that of Kohlrausch. 

 The one most like tbat of Kohlrausch has for 80° the number 

 2068, where Kohlrausch has 1833. At all events, with respect 

 to convenience as well as to accuracy of results, the method of 

 preparing Tables by torsion-measurements is preferable to all 

 others. It need scarcely be mentioned that these measurements 

 must not only be made in the manner indicated, but, as a verifi- 

 cation, repeated at every separate station. The quantities, too, 

 with which the raeasuremeuts are made must not be too great, 

 otherwise the torsion for 10° might be so great as to impair 

 the elastic reaction. A tolerably thick glass thread is better 

 than a very fine one, for air-currents and elastic reaction have 

 less effect upon it. The Tables being once prepared, measure- 

 ments of the tension of the pile serve well to verify the same. 

 When the tension remains pretty constant for some hours, the 

 measurements show a considerable agreement, provided a good 

 Table exists. For instance, on the 13th of April of the fore- 

 going year, the following successive values for the tension of an 

 element were obtained, \yherein the bracketed numbers denote 

 the number of elements : — 



3-16(128), 3-13(144), 3-17(160), 3-19(176), 

 3-20 (192), 3-21 (208), 3-23 (224), 3-25 (240), 3-27 (256), 

 3-26(240), 3-22(224), 3-19(208), 3-21(192), 3-17(176), 

 3-19(160), 3-19(144), 3-18(128), 3-15(112), 3-14(96), 

 3-14(80), 3-14(64), 3-10 (48), 3-06(32), 3-31(16). 



