444 



NATURE 



[June io, 1909 



cotton which is completely saturated with water may be 

 detonated by the detonation of dry gun-cotton in direct 

 contact with it used as a " priming charge," thus securing 

 a large margin of safety for the naval vessels carrying 

 the explosive. Wet gun-cotton containing as high as 

 35 per cent, of water has been shown to be a more elticient 

 rupturing and shattering explosive than dry gun-cotton, 

 but the question of how much water the discs of priming 

 gun-cotton could contain to be efficient was the object of 

 the_research detailed in this paper. The primer was in all 

 cases fired by the service detonator, containing 36 grains 

 of mercuric fulminate. The results show that detonation 

 of the entire charge was effected in every case in which 

 the primer contained less than 12 per cent, of moisture, 

 and occasionally was complete in cases where the moisture 

 ran as high as 15 per cent., and therefore that such gun- 

 cotton primers containing not more than 12 per cent, of 

 moisture, fired by means of a detonator containing 35 grains 

 of mercuric fulminate, may be relied upon to detonate 

 wet gun-cotton with which they are in contact. 



South American fossil Cetacea, Dr. F. W. True. Dr. 

 True remarked that, in connection with a revision of the 

 fossil whales and porpoises of the United States, he had 

 had occasion to examine various specimens from Patagonia. 

 Some of the Patagonian forms belong to families still 

 represented in South America by living species. Others 

 represent families no longer existing. The fossil fauna 

 includes sperm whales, various forms allied to the Inia, 

 others allied to Squalodon, and at least one species of 

 whalebone whales, allied to the finbacks, but no ziphioid, 

 or beaked, whales, nor any true dolphins, have been found. 



On the remarkable changes in the tail of comet c 1908 

 (Morehouse), and on a theory to account for these changes. 

 Prof. E. E. Barnard. The changes that occurred in the 

 tail of this comet appear to indicate resistance to the 

 passage of the body through space. In the discussion of 

 the paper it was suggested that this resistance might arise 

 from clouds of meteoric dust, too fine to be visibly appreci- 

 able, but still dense enough to offer a resistance that 

 would account for the changes in the form of the tail of 

 the comet. 



On the ruling of diffraction gratings. Prof. A. A. Michel- 

 son. The paper gave a brief statement of the development 

 of the grating. From the point of view of resolving 

 power, the important fact is not so much the number of 

 rulings per inch as the total number of rulings, and this 

 greater number of rulings necessitates a correspondingly 

 greater degree of regularity, an accumulated error of one 

 ruling in the entire number being fatal. The ruling engine 

 now set up in the Ryerson Laboratory gives this necessary 

 increase in perfection of ruling, so that the spectra are 

 almost free from ghosts, and those of the higher orders 

 can be used. The resolving power is proportional to the 

 product of the total number of rulings into the order. A 

 photograph of a part of the mercury spectrum was shown, 

 in which the distance between two of the lines was only 

 1/200 of the distance between the sodium (D) lines, and 

 it was evident that lines separated by only half this 

 distance would be distinctly resolved. This ruling engine 

 is the result of seven years' work. The large lo-inch 

 gratings are ruled on metal, to save the cutting edge of 

 the diamond, and weigh about 30 lb. The greater part 

 of this weight is supported by a float in mercurv, only 

 a small part pressing upon the ways. It is moved along 

 the ways by a screw with a large head working by fine 

 teeth in an automatically actuated worm. This screw was 

 made as perfect as possible by long, careful grinding, and 

 the remaining errors, which are of the order of the one- 

 millionth part of an inch, are automatically compensated 

 for by the slight tangential motion of the worm. This 

 motion is a function of the position of the nut, determined 

 empirically. 



Solar activity and terre.strial magnetic disturbances. Dr. 

 L. A. Bauer. This paper deals with the connections 

 between the various manifestations of solar activity, e.g. 

 sun-spots and the so-called magnetic storms which at times 

 affect compass needles simultaneously all over the earth 

 by several degrees, and even cause serious interruption in 

 telegraph and cable lines, and are usually accc.npanied by 

 fine auroral displays. One of the most "important of the 

 NO. 2067, VOL. Sol 



conclusTohs arrived at is that an increase in sun-spot activity 

 is accompanied by a decrease in the earth's magnetisation, 

 or that the magnetisation superposed on the earth's mag- 

 netic field during solar outbreaks is opposite to that of 

 the earth's own field. It appears questionable whether the 

 earth's magnetism ever settles down precisely to its former 

 condition after the occurrence of a magnetic storm. The 

 facts are not yet sufficient to draw a definite conclusion 

 whether solar activity and magnetic storms stand to each 

 other as cause and effect, or whether they are both effects 

 of the same cause. The indications are that during a 

 period of intense solar activity, in some as yet unknown 

 manner, considerable fluctuations are caused to take place 

 in the electric field that we know from various facts exists 

 in the regions above us. These varying electric currents 

 in turn affect the magnetic needles on the earth's surface. 



On the Hevelian halo. Prof. C. S. Hastings. The paper 

 reviewed the various kinds of halos that have been described 

 and the explanations that have been offered in regard tck 

 their origin. It had been assumed by writers on the sub- 

 ject that the snow crystals, which are in the form of 

 plates or prisms, would fall with the plate or prism pre- 

 senting the least resistance to the air. Thus, according 

 to this idea, the he.xagonal plates would fall edge on and 

 the prism end on. This was shown to be incorrect, and 

 the contrary was the case ; the plates and prisms could fall 

 through the air with their longer dimensions horizontal. 

 The plates would assume a horizontal position as well 

 as the prisms. The halo was then caused by total internal 

 reflection from the plates or prisms, and not by surface 

 reflection. Assuming these general positions for the long 

 or short prisms (or plates) and total internal reflection, the 

 various types of halo that have been described could be 

 explained, with the exception of the Hevelian halo. To 

 explain this on the basis of total internal reflection, it was 

 necessary to assume pyramidal planes in the crystal of 

 such an angle as to produce the 90-degree halo of this 

 rare type. 



The effect of temperature on the absorption of 

 certain solutions, Prof. H. C. Jones. Increase of tempera- 

 ture of the solution was found to alter the absorption 

 spectra in the same way that they are changed by con- 

 centration of the solution. 



Symposium on earthquakes. Prof. E. O. Hovey, Prof. 

 W. H. Hobbs, and Prof. H. F. Reid. Prof. Hovey's 

 paper served as an introduction to the subject. The ideai 

 in regard to the cause of earthquakes were considered, 

 especial attention being given to a discussion of volcanic 

 earthquakes. Prof. Hobbs pointed out the fact that the 

 seismic focus or centrum, as determined by the method of 

 Mallet, was at best a line, and practically had no exist- 

 ence. He explained the production of earthquakes by the 

 shifting of segments of the crust along already existing 

 fissures, and insisted upon the tectonic origin of earth- 

 quakes. Prof. H. F. Reid considered three phases 

 of the subject : — (a) conditions leading to tectonic earth- 

 quakes ; (b) instruments used in the study of earthquakes ; 

 (c) suggestions for a national seismological bureau. 



The burning bush and the origin of Judaism, Prof. F. 

 Haupt. The burning bush was explained as the shrubbery 

 on the heights of a volcano, lighted up at night by the- 

 glow of the incandescent lava. The story of the pilla- 

 of cloud by day and the pillar of fire by night was na~ 

 that it hung over the Tabernacle, but over Mount Sinai . 

 the cloud of steam from the active volcano was the "^pillar 

 of cloud by day and the pillar of fire by night." The 

 destruction of Jericho and of Sodom and Gomorrah were 

 attributed to earthquakes. 



.At the Darwin commemoration meeting, after the pre- 

 sentation of the three addresses, attention was directed to- 

 the fact that there are two members of the American 

 Philciophical Society still living in England who were 

 friends of Charles Darwin, Sir Joseph Dalton Hooker and 

 Dr. Alfred Russel Wallace. It was unanimously resolved 

 that the society should cable to them its greetings and 

 congratulations on the general acceptance of the views 

 in the elaboration and promulgation of which they had 

 taken such an effective part. 



The following resolutions were adopted in the course of 

 the meeting : — (i) Whereas the L'nited States in former 



