ATMOSPHERIC ELECTRICITY AND OZONE. 457 



As I laid down the paper I asked myself this question, or, rather, 

 I put to myself the same question in another form: "Is there among 

 the sons of men any one who really knows the composition of pure 

 air?" 



Still further I queried with myself what answer I should have 

 given to the question had I been one of the applicants for a position 

 on the Board of Health, and it seemed to me that, after stating what 

 almost every school-girl knows about the relative proportions of oxy- 

 gen and nitrogen, I should have added this codicil : " The question 

 of the composition of pure air is one that is too complicated to ad- 

 mit of an answer." What I have to say this morning on atmos- 

 pheric electricity and ozone will serve, so far as it goes, to enforce 

 this view. 



How the Subject of Atmospheric Electricity and Ozone has been 

 investigated. — During the past quarter of a century regular daily ob- 

 servations of atmospheric electricity have been made in Brussels, 

 Munich, and for the past ten or fifteen years in St. Louis. The diffi- 

 culties in the study of the subject are very great, but, from the accu- 

 mulated observations of the different investigators, some few interest- 

 ing and important general facts have been secured. 



Apparatus for studying Atmospheric Electricity / Measuring Appa- 

 ratus. — Prof. Dellman, of Kreuznach on the Rhine, for several years 

 made three regular observations each day of the atmospheric electri- 

 city. The electrometer that he used in these observations is a torsion 

 balance. A small thread of glass going vertically through a glass 

 tube has on its lower extremity a small needle of brass fastened to it. 

 This light brass needle, when influenced by any force, can move over 

 a metallic disk with a graduated scale. Below this light brass needle 

 is another light brass needle, which is fixed and isolated from the me- 

 tallic disk, and connected with a metallic wire which receives the elec- 

 trical charge from outside. By means of a micrometer screw the up- 

 per needle can be lowered and raised so as to touch the lower needle, 

 or be kept above it. 



The whole instrument rests on three iron legs, which can be 

 screwed up and down so as to give it the level required. When 

 the wire outside receives a charge of electricity, it communicates 

 this charge to the lower needle. If, now, the upper needle be low- 

 ered and brought in contact with the lower one, it also receives a 

 charge of electricity. But, as like electricities repel each other, the 

 other needle will be at once driven off" over the graduated scale. The 

 number of degrees that it is driven will depend on the strength of the 

 charge. To determine whether the electricity is positive or negative, 

 subsequently charge the wire with electricity of known quality. If 

 they are alike — that is, if the first charge be of the same quality as 

 the second — the needle will be repelled still farther; if unlike, the 

 needle will return toward the fixed needle. 



