May II, 1-9163 



NATURE 



229 



Of course, if the sun sets behind a sloping- hillside, the 

 duration may be considerably altered by this cause. 



The March number of Terrestrial Magnetism and 

 Atmospheric Electricity contains a table by Mr. J. P. 

 Ault of the values of the deviation of the 

 compass from true north in the Bering Sea and 

 the Pacific Ocean, determined by the magnetic survey 

 ship Carnegie during her voyage from Alaska to New- 

 Zealand in the latter half of 1915. Throughout the 

 whole of her course, which from the western side of 

 the Bering Sea was almost directly south, the com- 

 pass pointed to the east of true north by amounts vary- 

 ing from half a degree in latitude 45° N. to 16° or 

 17° at Alaska and New Zealand. The British Admiralty 

 charts give the compass deviation too high by amounts 

 which, in the Bering Sea, exceed a degree, and in 

 latitudes 37°, 21°, 14°, 12°, 0° N., 15° and 45° S. are 

 nearly a degree. 



Bulletin 609 of the United States Geological Survey 

 deals with the fractional precipitation of some ore- 

 forming compounds at temperatures only slightly re- 

 moved from atmospheric, and in all cases below 

 100° C, by Mr. R. C. Wells. The experiments have 

 been made with the object of elucidating the chem- 

 istry of ore deposition, and they have shown the order 

 of solubility of the compounds of each of the classes 

 investigated — sulphides, hydroxides, carbonates, and 

 silicates. On the whole, the most interesting, and 

 probably the most complicated, series is that of the 

 sulphides. Soluble sulphides may act, and do act, 

 not only as precipitating, but also as reducing agents. 

 It appears from the results given that the concen- 

 tration of the sulphide ion is so greatly affected by 

 change of acidity that the latter is the principal factor 

 determining the precipitation of sulphides. A mixture 

 of two metallic salts yields, by fractional precipitation, 

 an initial precipitate, containing the sulphides of both 

 metals, but, as a rule, if the mixture is heated or is 

 permitted to stand, one sulphide largely or wholly 

 dissolves. The order of precipitation, beginning with 

 the metal that separates first, is palladium, mercury, 

 silver, copper, bismuth, cadmium, antimony, lead, 

 zinc, nickel, cobalt, ferrous iron, arsenic, thallium, 

 and manganese. Attempts to form chalcopyrite by 

 fractional precipitation of ferrous and cupric sulphate 

 were unsuccessful. 



Paper No. 33 of the Survey Department of 

 Egypt, entitled "The Magnetic Survey of Egypt and 

 the Sudan," by Mr. H. E. Hurst, embodies the results 

 of field observations made by the author and Mr. C. B. 

 Middleton between October, 1908, and January, 1914. 

 Use is also made of observations taken between 1893 

 and 1901 by Captain (now Major) H. G. Lyons, 

 F.R.S., and of the results obtained in the Red Sea 

 between 1895 and 1898 by Lieut. Rossler, of the Aus- 

 trian surveying ship Pola. The publication includes 

 charts of magnetic declination, inclination, and hori- 

 zontal force respectively. The epoch to which the 

 observations are reduced is January i, 1910. Helwan, 

 where magnetographs were installed in 1907, served 

 as base station. The area dealt with extends from 

 Damietta, 31° 25' N., to Wadelai, 2° 42' N. lat. ; but 

 it is comparatively narrow, especially in the extreme 

 south. A remarkable feature is the closeness with 

 which the lines of equal dip — from 42° N. to 16° S. — 

 conform to parallels of latitude. The magnetic equator 

 crosses the Nile at about 11° N. lat. The lines of 

 equal declination have mostly throughout the greater 

 part of their length the same general direction as the 

 Nile. The lines of equal horizontal force, from 0*295 

 to 0-350 C.G.S., seem to cross the Red Sea nearly 

 orthogonally. The local disturbances encountered 

 were extremely small, especially in comparison with 



NO. 2428, VOL. 97]' 



those described by Prof. J. C. Beattie in his "Mag- 

 netic Survey of South Africa." 



A COPY of the report of the secretary of the Smith- 

 sonian Institution for the year ending June 30, 1915, 

 has been received. The report reviews the affairs of 

 the institution, and summarises the activities of its 

 several branches. Among the explorations and re- 

 searches inaugurated in furtherance of one of the 

 fundamental objects of the institution, which is the 

 "increase of knowledge," we notice the clearing of fog 

 by electrical precipitation. The fact was long ago 

 established that all dust and fog particles in the open 

 atmosphere are electrified and subject to dispersion 

 or precipitation, but how to clear fog from a street, 

 along a railway, or from the neighbourhood of a ship 

 at sea, and to do it in a manner commercially feasible, 

 has been a matter of study for many years. The ques- 

 tion recently aroused fresh attention in the neighbour- 

 hood of San Francisco, through researches planned by 

 the University of California in co-operation with the 

 United States Lighthouse Service, and it was decided 

 by the Smithsonian Institution to make a grant to 

 further this investigation, which is under the general 

 direction of Dr. F. G. Cottrell. The American Insti- 

 tute of Electrical Engineers has also appointed a com- 

 mittee to co-operate in this work. The essential 

 element to success in scattering fog seems to be some 

 form of electrical apparatus of very high direct voltage, 

 with facilities for its control and ready application. 



The H. VV. Wilson Company, White Plains, New 

 York, has published a supplement to the " Readers' 

 Guide to Periodical Literature," which forms an index 

 to general periodicals not included in the guide. The 

 periodicals indexed in the supplement include Nature, 

 the Hihbert Journal, the Philosophical Review, and 

 others published in this country. 



OUR ASTRONOMICAL COLUMN. 



Uranus. — This planet is now an early morning 

 object in the constellation of Caprioomus. When its 

 position is known it is easily visible with quite small 

 apertures; thus on .\pril 29 it was seen with a hand 

 telescope of ig in. opening, at G.M.T. 3h. 34m. The 

 dawn had then, of course, overpowered all stars in 

 the region. On May 12 the position of Uranus will 

 be R.A. 2ih. i3-2m., declination —16° 476', diameter 

 3-8''. 



Mercury. — On September 21 of last year Mercurj' 

 passed within i' of Spica, and a long series of posi- 

 tional measures was secured at the Union 

 Observatory, Johannesburg (Circular No. 30). 

 The observations made by Messrs. Innes and 

 Worssell with a 9-in. refractor possess excep- 

 tional interest, as both observers agree regard- 

 ing the visibility of a small N. polar cap and an 

 indistinct band south of it. This appears on the 

 reproductions as a narrow dusky zone in about latitude 

 45°. .\s an index to the conditions under which the 

 observations were made, it may be stated that the 

 conjunction occurred six days prior to elongation, the 

 diameter of the slightly gibbous disc being 6-2*. The 

 data indicate that the approximate G.M.T. of con- 

 junction was 2h. 57m. 42s., when the zenith distance 

 of Spica would be 51° 4' at the Union Observatory. 

 The truncated cusp recorded by other observers may 

 perhaps find an explanation in this Johannesburg 

 observation. 



The Lyrid Meteors of 19 16. — Mr. W. F. Denning, 

 writing from 44 Egerton Road, Bristol, says : — 

 Cloudy weather seriously interfered with the observa- 



