62 Observations on some Experiments in Electricity. 



with a dew-point in spring at 39.41°, we have an excess of tempe- 

 rature of 12^°, whereas in autumn with a dew-point at 46.46°, we 

 have a mean excess of only 8.54° ; — hence, both causes conspire 

 in favor of spring and against the autumn. The mean quantity 

 of moisture in the cubic inch of air in spring, is .00174764 while 

 that in autumn is .00220070, or about twenty-five per cent, more 

 moisture, and one-third less excess of temperature in the latter than 

 in the former. If we suppose experiments to be made in winter in 

 an apartment artificially heated to 70° while its dew-point remains at 

 23.25°, we shall have an excess of 46.25°, and as before, a quantity 

 of moisture expressed by .00103359. If under these circumstances, 

 the dryness could be maintained constant, electrical experiments 

 might be performed with great satisfaction, but as lecture rooms are. 

 sometimes furnished with pneumatic cisterns, and other sources of 

 vapor, as well as occupied by numerous classes, the dew-point rises, 

 more or less rapidly, far above that of the surrounding air without. 

 The truth of this statement may have often been perceived by 

 persons who wear spectacles, on which the moisture was con- 

 densed as they entered, from a cold atmosphere, an apartment at 

 a high temperature, crowded with company, or furnished with other 

 sources of moisture. It may also have been observed that a machine 

 will sometimes work well soon after a fire has been lighted, but will 

 lose its power rapidly as the company before whom it was to be ex- 

 hibited, come together, and further, that it will temporarily regain its 

 activity by opening a door for a short time and admitting a supply of 

 dry though cold air. 



The substance of the foregoing remarks and calculations may be 

 presented in a tabular form, exhibiting moreover the ratios for the se- 

 veral seasons between the moisture at the dew-points and the excess 

 of temperature by which it is accompanied. The seasons are arrang- 

 ed in the order of the ratios, beginning with the least favorable. 



