66 LOMBARD :
may well have an influence upon man. There can be no doubt but that the degree of the humidity of the atmosphere influences us greatly by determining the evaporation of the perspiration from the skin, but that we are influenced by the electrical condition of the atmosphere is by no means as certain. One knows so little concerning the electrical changes of the air that the subject is always an attractive theme for speculation, and one is in the habit of holding it responsible, in a vague sort of way, for many peculiar feelings which he cannot otherwise explain. The idea is a popular one and even finds its way into the novel of the day. Thus, one reads: "I hastened to do as I was asked, the more readily as, what with fear and horror, and the electric tension of the night,
I was myself restless and disposed for action." 1 Plate II was constructed to enable one to readily
compare the variations of the knee-jerk with the changes which all the different components of the weather underwent at the same time.
The study of the electrical condition of the atmos- phere is a difficult one and requires the use of special appliances. The writer could, therefore, scarcely have gained any information on this point had it not been for the kindness of Mr. Park Morrill, who was making a special study of this subject near by, at the Johns Hopkins University. The curve of the electric potential of the atmosphere given in the chart is based on Mr. Morrill's figures, which state in volts the elec- tric potential of the air as compared with that of the earth, regarded as 0.
Explanation of Plate II. — On the first line, at the top, are given the dates, and beneath them the hours of the day, from 7 A. M. to
II P. M.
1 The Merry Men, by R. L. Stevenson.
