324 CARNEGIE INSTITUTION OF WASHINGTON. 



in the night portion, judging from the place where the corresponding solar 

 observations are made. This is being looked into further. 



It is seen that at the maximum a change in the magnetic constant, G, of 

 about 10X10"^ C. G. S. might be associated wth such changes in the solar 

 radiation as are sho^vn by Abbot's solar-constant values. However, during 

 even a moderate magnetic storm G has changed lOOXlO"^, and during a 

 severe one, 1000X10"^, or 1X10~^, or by about ^jV (and even more) of its 

 absolute amount. Magnetic storms can not, therefore, in general, be asso- 

 ciated with changes in the solar radiation as measured by the solar constant. 

 But there is a certain class of magnetic perturbations which, though sudden in 

 appearance at any one station, do not occur simultaneously over the globe, but, 

 instead, each time the disturbance occurred, only the observatories in the 

 daylight zone recorded it. The change in the magnetic constant, G, for a 

 typical disturbance of this class and on the average for the various observa- 

 tories over the globe, is about 10X10-^ C. G. S., which is the amount that 

 might be associated with a 10 per cent change in the solar radiation. If there 

 are observable changes in the Earth's magnetism, associated with changes of 

 solar radiation, then it is not surprising that magnetic observatories should 

 continually be recording magnetic perturbations even on apparently undis- 

 turbed days, as, for example, the "elementary waves," or "magnetic pulsa- 

 tions," forever occurring during periods of absolute solar calms, as gaged by 

 absence of sun-spots. 



In the discussion of magnetic disturbances we may have to distinguish 

 between two broad classes: 



(1) The curvilinear, the more prominent as far as general magnitude is 

 concerned, occurring practically over the whole Earth at the same time, 

 seemingly initiated by streams of charged particles which are deflected from 

 a straight path, when they come under the influence of the Earth's magnetic 

 field, as to pass bej^ond and behind the sun-lit portion of the Earth. 



(2) The rectilinear, occurring practically only over the portions of the Earth 

 reached by the ordinary light radiations from the Sun. 



The atmospheric-electric observations made on the second cruise of the Carnegie, 1909-1913. 

 Report by C. W. Hewlett. Terr. Mag., vol. 19, pp. 127-170 (1914). " 



The atmospheric-electric observations, of which an account is given in this 

 report, were made in pursuance of the plan of work assigned to the Carnegie by 

 the Director of the Department of Terrestrial Magnetism. The observers 

 received at all times the cordial support of Mr. W. J. Peters, while in command 

 of the vessel. The final reduction and discussion of the observations have 

 been made under the direction of Dr. W. F. G. Swann. 



The atmospheric-electric work on board the Carnegie has been confined 

 entirely to observations of the specific conductivity, the potential gradient, 

 and the radioactivity of the atmosphere, the greater part of the observations 

 consisting of the first two quantities named. The observations are divided 

 naturally into three principal groups, according to the observer who made 

 them. From New York to Colombo, E. Kidson conducted the observations; 

 for the route from Colombo to Manila, owing to breakage in the instruments 

 and the impossibility of having the requisite repairs made, there are no 

 observations; from Manila to Tahiti, H. F. Johnston conducted the obser- 

 vations, and from Tahiti to New York, the work was carried on by C. W. 

 Hewlett. For an account of the instruments and methods used, reference 

 must be made to the original article. 



The mean values of the total conductivity, the ratio of the positive to the 

 negative conductivities, and the relative potential gradients are given in 

 table 2. The conductivity is expressed in electro-static units. 



