252 



NATURE 



[November 29, 19 17 



contained a considerable amount of potassium salt as 

 detected by the flame test. After four recrystallisations 

 from distilled water, however, the purified salt con- 

 tained only o-oi per cent, of potassium chloride. A 

 sample prepared and purified in the same way, except 

 that caustic soda "pure by alcohol" was employed, 

 contained 0-03 per cent, of potassium chloride, whilst 

 four recrystallisations of a sample of "C.P." common 

 salt gave a product containing 007 per cent, of the 

 same impurity. The chief conclusion drawn is that 

 although pota"ssium chloride obstinately persists with 

 sodium chloride, it can be remoyed by repeated re- 

 crystallisations. 



A GREAT deal of information is contained in a paper 

 on gas-firing boilers read by Mr. T. M. Hunter at the 

 Institution of Electrical Engineers on November 22. 

 Mr. Hunter believes that there is a great future for this 

 method of firing boilers, despite the unfortunate ex- 

 periences which have been the lot of many engineers 

 in the past. Mr. Hunter's paper — which is almost a 

 text-book on the subject — should assist engineers to 

 understand and to obtain the proper conditions for 

 economical gas-firing. In connection with the testing 

 of results, the following extract is of interest: — "The 

 apparatus for boiler control will cost a considerable 

 amount, and it must not be overlooked that the best 

 outfit of recording instruments is useless unless a 

 constant and intelligent use of them is enforced abso- 

 lutely. If, in addition to this, the boilermen and the 

 man in charge of the boiler plant are given a premium 

 for maintaining good results, boiler control will soon 

 develop into a fine art, and prove an important source 

 of revenue." We think that Mr. Hunter's remarks 

 should be noted by owners of boilers. There are 

 numerous cases where CO2 recorders, pyrometers, etc., 

 have been installed, and are practically ready for the 

 scrap heap after a few weeks' life, when they have 

 served much the same purpose as toys. On the other 

 hand, if these instruments are kept in thorough work- 

 ing order, and if the workmen are taught to take an 

 intelligent interest in their records, it is astonishing 

 what improvements can be effected in the working of 

 the plant. 



We have received a small booklet from Messrs. Wat- 

 son and Sons (Electro-Me"dical), Ltd., of 196 Great 

 Portland Street, W.i, entitled "The Sunic Record," 

 dealing with some recent developments in the produc- 

 tion of apparatus for the generation and application of 

 X-rays. The work is edited by Mr. T. Thorne Baker, 

 and is an interesting indication of present activity in 

 the British electro-medical industry. In addition to the 

 description of new apparatus the booklet contains 

 an original article on the suppression of the "inverse" 

 current in induction coils, notes on the X-ray examina- 

 tion of metal castings, radio-active paints, the Coolidge 

 X-ray tube, reviews of books, etc. It is proposed to 

 continue the publication monthly, and the proprietors 

 undertake to send copies to those who will forward 

 their names and addresses. 



Messrs. H. K. Lewis and Co., Ltd., 136 Gower 

 Street, W.C.i, have sent us a list of the new books 

 and new editions added to their Medical and Scientific 

 Circulating Library during July, August, and Septem- 

 ber. As the library contains upwards of 13,000 works 

 dealing with medicine, surgery, astronomy, biology, 

 botany, chemistry, electricity, engineering, geology, 

 microscopy, mining, physics, philosophy, sociology, 

 technology, voyages and travels, zoology, etc., and as 

 any recent book of importance which may be applied 

 for, if not already available, is added to it, it should be 

 of great service to science workers. The list will be 

 sent to any address on application. 



NO. 2509, VOL. 100] 



OVR ASTRONOMICAL COLUMN. 



The Total Eclipse of the Sln, June 8, 1918. — The 

 total eclipse of the sun on June 8, 1918, will be visible 

 in the United States along a belt having a maximum 

 breadth of sixty miles, extending from the State of 

 Washington, through parts of Oregon, Wyoming, and 

 Idaho, across Colorado and Kansas, and finally reach- 

 ing Florida about sunset. The duration of totality 

 will diminish from 2m. 2s. at the coast of Washington 

 to less than half that amount in Florida. It is reported 

 in Science (October 26) that Profs. Frost and Barnard 

 have made a personal investigation of certain localities, 

 and have decided upon Green River, Wyoming, as the 

 principal station for the expedition from the Yerkes 

 Observatory. Green River is situated between Chey- 

 enne and Ogden, in the so-called Red Desert, and with 

 a rainfall of about 10 in. per year, and an elevation 

 of 6000 ft., it appears to be one of the most promising 

 stations along the belt of totality. The transparency 

 of the air on the day of the visit of the Yerkes astro- 

 nomers is described as extraordinary. Denver is a 

 possible observing station, but there appears to be some 

 risk of cloud in the Colorado mountains on a June 

 afternoon. It is probable, however, that a spectro- 

 graph from the Yerkes Observatory will be attached 

 to the 20-in. equatorial of the University of Denver. 

 Another site very favourably reported upon is near 

 Matheson, Colorado, about sixty miles south-east of 

 Denver, at an elevation of 6000 ft. On account of the 

 war no British expeditions have been organised for ob- 

 servations of this eclipse. 



Reports of French Observatories. — From the 

 official report on the provincial observatories of France 

 for 19 16 it appears that a large amount of valuable 

 work has been carried on, in spite of the serious deple- 

 tions of stal? which are recorded. Meridian observa- 

 tions, observations of minor planets and comets, and 

 work connected with the astrographic chart of the 

 heavens are prominent features of the reports. Con- 

 siderable attention has also been devoted to terrestrial 

 magnetism and meteorology. At Lyons M. Luizet 

 has continued his important studies of short-period 

 variables, and numerous observations of double stars 

 have been made by M. Montangerand at Toulouse. 

 The retirement of M. Coggia is announced by the direc- 

 tor of the Marseilles Observatory; M. Coggia joined 

 the staff of this observatory in 1866, and was the 

 discoverer of seven comets, of which Comet VII. (1873) 

 and Comet III. (1874) were especially notable. 



Structure of Planetary NEBUt^. — ^An investigation 

 of the internal movements and possible structure of the 

 planetary nebulae 6543 and 7009 of the N.G.C. has been 

 made by Mr. W. K. Green (Lick Observatory Bulletin, 

 No. 298). In each case several long-exposure photo- 

 graphs of the spectrum were taken with different orien- 

 tations of the slit, so as to give the radial velocity at 

 a large number of points. The central portion of each 

 nebula gives direct evidence of rotation about the 

 shorter axis, but the outer portions along the major 

 axis seem to be rotating in the opposite direction, and 

 some of the observed velocities follow no regular law. 

 Photometric measurements of plates obtained with the 

 Crossley reflector have been made, and curves are 

 given showing the distribution of intensity along vari- 

 ous diameters. Both sets of observations point to a 

 rotating ellipsoidal shell as a possible form, but the 

 luminosity curves which have been calculated for such 

 forms are in disagreement with the observations as 

 regards the major axis. An attempt is made to ex- 

 plain the reversal of direction of rotation at the outer 

 ends by supposing that the central ellipsoid is sur- 

 rounded by a fainter ellipsoidal shell or ring, which 

 rotates in the opposite direction, but this hypothesis is 

 not considered to be entirely satisfactory. 



