November 4, 19 15] 



NATURE 



271 



equation, will serve to determine the values of v and i \ 

 for any particular case, and are sufficient for the pur- 

 pose. The author gives several numerical applica- 

 tions of this theory, which appears to be of general 

 application in the selection of speeds in plain and 

 internal work. 



The Engineering Magazine for October contains an 

 article on the forests of the United States, by Mr. 

 Leonard Lundgren. Before the coming of the white 

 man these forests covered an area of about 800 million 

 acres, and contained about 5200 billion board feet of 

 lumber. Fire has destroyed as much timber as has 

 been utilised for industrial purposes, and as much 

 again has been wasted through poor logging and 

 milling operations, and through clearing land for agri- 

 cultural purposes. The forests at present cover an 

 area of 550 million acres, and contain about 2900 

 billion board feet of lumber. Seventy-six per cent, of 

 this is owned privately, 21 per cent, is held by the 

 United States in the national forests, and 3 per cent. 

 is on other public lands. The annual cut is approxi- 

 mately 43 billion board feet ; at this rate, if there were 

 no new growth and the present demand were main- 

 tained, the timber supply would last about sixty-five 

 vears. It is reasonable to expect that all agricultural 

 lands, cultivated or uncultivated, will ultimately be 

 placed under crops that will give the greatest economic 

 return. Some of the lands now under cultivation will 

 unquestionably revert to forest. Through reducing the 

 per capita consumption (at present amounting to 260 

 cubic feet of wood per inhabitant), protection against 

 fire, and increasing the natural growth per acre by 

 the practice of forestry, it is probable that a balance 

 between production and consumption will eventually be 

 reached by the force of natural economic laws. In 

 Saxony, where forestry has been practised for many 

 years, the annual production is 93 cubic feet per acre. 

 Forestry is practised in the United States on Govern- 

 ment and State lands only, and the estimated annual 

 production is 12 cubic feet per acre. 



Messrs. Constable and Co., Ltd., 10 Orange 

 Street, London, W.C., inform us that they now pub- 

 lish in this country, at 6^. 6d. net, Prof. L. T. More's 

 "The Limitations of Science," reviewed in the issue of 



(Nature of September 2 last (vol. xcvi., p. 3). 

 • OUR ASTRONOMICAL COLUMN. 



The Andromeda Nebula. — According to a notice in 

 the September Journal of the Royal Astronomical 

 Society of Canada, a determination made at Mount 

 Wilson of the radial velocity of this nebula indicates 

 a recessional motion of 329 km. /sec. from measures 

 of nine lines. The spectrogram was obtained on five 

 consecutive nights during last November (thirty-four 

 hours' exposure), by means of a small slit spectrograph 

 at the primary focus of the 6o-in. reflector. There is 

 stated to be no evidence of either bright lines or rota- 

 tional displacement. 



A Long-Period Spectroscopic Binary. — Mr. J. B. 

 Cannon has made a determination of the orbital 

 elements of fx Persei, a spectroscopic binary having 

 the somewhat long jseriod of 284 days. The spectrum 

 is of the solar type, and a number of lines being avail- 



NO. 24.01. VOL. q6"1 



able for measures, a good determination of velocity 

 could be made. Forty-eight plates secured during 

 1913-15 were measured, and combined to give o-ii 

 normal places, the velocity-curve coming out very 

 nearly symmetrical. A range of velocity of 41 km. 

 is indicated, whilst 39 km. was found from seven 

 Lick spectra. 



Sun-Spots and Temperatures.— In continuation of 

 the statistical investigation of the question of seasonal 

 variations of weather Dr. Gilbert T. Walker publishes 

 (Memoirs of the Indian Meteorological Department, 

 vol. xxi., part xi., p. 61) a paper giving the correlation 

 coefficients of sun-spots with temperature for a large 

 number of stations generally distributed over the 

 earth's surface. A paradoxical defect of temperature 

 associated with times of maximum sun-spots is re- 

 vealed for a large number of stations, more especially 

 tropical. An area of positive coefficients, however, 

 stretches from the Arctic over the western parts of 

 Europe. 



The Union Observatory.— Circulars Nos. 26 and 

 27 have recently come to hand. The first of these 

 gives details in continuation of the investigation by 

 blink-microscope of the variable stars in the region of 

 »j Argus. A table is given showing the results of 

 special search for known variables not picked up in 

 the first survey. The variability of a star (R.A. 

 loh. 9m. 36s., declination -58° 243' (1875), announced 

 last year by Dr. A. W. Roberts, is confirmed. 



In the other circular Mr. J. Voute gives the results 

 of measures of sixty-seven double stars, employing the 

 Bosler-Salet inverting prism to eliminate systematic 

 errors in the measurement of position angles. The 

 instrument used was the 9-in. Grubb refractor. It 

 was specially desired to obtain experience of the work- 

 ing of the method under additional instrumental condi- 

 tions in extension of measures made at Leyden and 

 at the Cape. In this process the position-angle is 

 determined as the mean of measures made before and 

 after inverting the field by means of a prism. The 

 present results are in good agreement with the Leyden 

 series, amply supporting the favourable opinions re- 

 garding the method. 



A message from the observatory, dated October 7, 

 informs us that a 12th magnitude star, with 

 a proper motion of 51" a year, has been found with 

 the blink apparatus. Full particulars will be given in 

 a forthcoming Union Observatory Circular. The place 

 of the star is (1900) R.A. i4h. 22-9171., declination 

 -62° 2'. 



The Orbit of B.A.C. 5890. — A noteworthy spectro- 

 scopic investigation of this binary system has been 

 made by Mr. F. H. Parker at the Dominion Observa- 

 tory, Ottawa {Jour. Roy. Astr. Soc, Canada, Sep- 

 tember). The reductions are based entirely on pairs of 

 measures made on plates showing spectra of both 

 components. Nineteen such plates were secured at 

 Ottawa, but the dispersion only sufficed to separate 

 the lines near primary maximum. However, one of 

 three Lick spectra showing double lines was taken 

 near apastron, thus fortunately bridging the gap. 

 The measures of the Canadian plates were grouped 

 into five normal places, those from the Lick plates 

 giving three additional points. The photographic 

 magnitude of the star is 49, the spectrum being of 

 the F type, and the lines are described as " broad." 

 The masses of the components are very nearly equal 

 (25 : 24). The period is 2627 days, whilst the eccen- 

 tricity has the rather large value 049. This is not 

 altogether exceptional, for, curiously enough, binaries 

 having periods 12-30 days yield an average value of 

 0462, according to the data recently collected by 

 Dr. Sven Wicksell. 



