98 Scientific Intelligence. 



fore, it will be sufficient to state that the book contains four 

 "Dialogues" which deal with the following subjects : "I. First 

 new science, treating of the resistance which solid bodies offer to 

 fracture. First Day ; " " II. Concerning the cause of cohesion. 

 Second Day ; " " III. Second new science, treating of motion 

 [movimenti locali]. Third Day. Uniform motion. Naturally 

 acclerated motion ; " and " IV. Violent motion. Projectiles. 

 Fourth Day." h. s. u« 



12. The Norwegian Aurora Polaris Expedition, 1902-1903. 

 Vol. I. On the Cause of Magnetic Storms and the Origin of 

 Terrestrial Magnetism ; by Dr. Birkeland. Second section. 

 Pp. ix, 319-801, pis. XXII-XLII. Christiania, 1913.— The first 

 section of this extended work by Dr. Birkeland, based upon 

 observations made during the polar expeditions of 1896-1903, was 

 published five years since and noticed at length in this Journal at 

 the time (volume xxix, p. 272). The second section, now issued, 

 carries forward the subject, Part II being devoted particularly to 

 " Polar Magnetic Phenomena and Terrella Experiments " ; and 

 Part III to "Earth Currents and Earth Magnetism." Numerous 

 special plates accompany the volume; these are devoted in part to 

 the perturbations observed from October 15, 1882, to July 15, 

 1883; also others to earth currents and magnetic elements at 

 Kaaf jord, Bossekop, Pare St. Maur, Greenwich, etc. The author's 

 point of view and conclusions can be best brought out by the 

 following quotations from the preface : 



" In order further to make it clear whether our results from the 

 working-up of the above-mentioned observations from the most 

 varied parts of the world could be brought into theoretic harmony 

 with my previous assumptions, I have carried out a long series of 

 experimental investigations with a magnetic globe in a large 

 vacuum-box intended for electric discharges. I have hereby been 

 enabled to obtain a representation of the way in which cathode- 

 rays move singly, and group themselves in crowds about a mag- 

 netic globe such as this. Special study has been made of those 

 crowds of rays that produce magnetic effects analogous to those 

 observed upon the earth during positive and negative polar 

 storms." * * * 



" I hold that I have demonstrated that the magnetic storms on 

 the earth — the positive and negative polar storms, and the posi- 

 tive and negative equatorial storms — may be assumed to have as 

 their primary cause the precipitation toward the earth of helio- 

 cathode rays, of which the magnetic stiffness is so great that the 

 product H. p for them is most usually about 3 X 10 6 C. G. S. units. 



"On account of the magnetic condition of the earth, these new 

 solar beams which I have discovered will especially make their 

 way towards the earth in the polar regions in the two auroral 

 zones, where they also certainly produce other effects which play 

 an important part in various meteorological phenomena," 



