594 



NATURE 



[June 29, 1911 



adopted. Mr. Mall finds differences in the values obtained 

 for the height accordinfj to the time of day and the season 

 of the year at which the observations of pressure, tempera- 

 ture, and humidity are made. The values are generally 

 larger near midday and in summer than at other times 

 and seasons, a result not altogether surprising. The 

 tempi r;iuiii' i ni- iv inin ilie determination of height through 



the expression / ' ,'» Jind there is clearly room for error 



if this is taken to be (s, — c,)/T.( where T.\i= J(T,4-T,) and 

 T,, Tj are the temperatures at the lower and upper stations 

 respectively. Mr. Hall elaborates an empirical method for 

 correcting the value of Tm obtained in this way, in order 

 to eradicate the differences found. In this connection it 

 may be mentioned that recent determinations of heights in 

 the Tyrol have furnished results closely agreeing with the 

 values obtained by levelling. In these cases, however, 

 mean values were used, and an intermediate station was 

 available. Mr. Hall uses the value 60,159 feet in the 

 hypsometric formula, instead of 60,369 feet, the value 

 adopted in the International Tables, but does not state his 

 reason for preferring the smaller value. 



In The Electrician for June 9, Dr. R. Beattie describes 

 a method of determining the coefficients in the Fourier 

 series for a curve, which should extend the use of such 

 series amongst those who have not had a mechanical 

 analyser at command and have been unwilling to go 

 through the laborious process of determining the coefficients 

 arithmetically. It will be remembered that the latter 

 process consists in measuring the ordinates of the curve at 

 regular intervals, multiplying these by the sines or cosines 

 of certain angles, and taking the mean of the products. 

 Dr. Beattie 's suggestion is to measure the ordinates on 

 scales graduated so as to read the products direct, and 

 thus reduce the work to addition. Once the necessary 

 scales are available the method will, we anticipate, be used 

 extensively. 



The Department of Commerce and Labour, Coast and 

 Geodetic Survey, Washington, has issued a volume of 

 " Directions for Magnetic Measurenients," by Mr. Daniel 

 L. Hazard, of the Division of Terrestrial Magnetism. 

 This extends to 131 pages, and contains instructions for 

 the absolute observation of the magnetic elements with 

 instruments of the various types used by the Coast and 

 Geodetic Survey. The instruments are described with 

 illustrations, and there is a discussion of the determination 

 of the several constants. This is followed by a series of 

 " directions for operating a magnetic observatory," which 

 includes an account of Eschenhagen magnetographs and 

 the methods of standardising the curves. At the end there 

 are a series of tables intended to assist in the reduction of 

 the absolute observations, which include some particulars 

 of the diurnal inequalities recorded at the observatories 

 belonging to the Coast and Geodetic Survey. 



The U.S. Coast and Geodetic Survey's *' Results of 

 Magnetic Observations made . . . between July i, 1909, 

 and June 30, 19 10," gives in about seventy pages an 

 account of a year's work in terrestrial magnetism in the 

 United States. Observations were made at 241 stations, 

 including a number previously occupied, so that numerous 

 secular change data were obtained. A good many mag- 

 netic observations were also made at sea by the Survey's 

 vessels. Two-thirds of the space is devoted to descrip- 

 tions of the stations occupied. The situation of some of 

 these seems a little unusual. Several, for instance, are In 

 cemeteries, the exact site being marked by small pillars 



NO. 2174. VOL. 86] 



dated and lettered U.S.C. and G.S., the coordinates of 

 which in some cases are given in terms of the distancets 

 from adjacent tombstones. If the absence of iron can b- 

 relied on, and sentiment does not count, it cannot b. 

 denied that a good deal can be said in favour of the 

 practice, but one rather wonders how it strikes the average 

 unscientific American. 



The June issue of J cm-slrial Ma^rnlmn and ilmu- 

 spheric Electricity contains particulars of comparisons of 

 magnetic instruments made by observers of the Carnegie 

 Institution, Washington, between 1905 and 1910, at a 

 number of stations in North and South America, .Asia, 

 .Australia, and Europe. It also gives voluminous lists of 

 data which the editor. Dr. Bauer, has received from a 

 number of observatories in response to a request for in- 

 formation as to the exact times of commencement of fifteen 

 magnetic disturbances which occurred between 1906 and 

 1909. The object is to settle a controversy which took 

 place recently in the columns of Nature as to the rate of 

 propagation of these disturbances round the earth. A 

 further list of data is to appear in the next number of the 

 magazine. The discussion by Dr. Bauer will be awaited 

 with interest. In a reference to the meeting of the Inter- 

 national Meteorological Committee, held last September in 

 Berlin, the removal of atmospheric electricity from the 

 domain of the Commission on Terrestrial Magnetism is 

 adversely criticised. A reference to the " passing of the 

 Kew Magnetic Observatory " leads to the statement that 

 " the testing and standardising of magnetic instruments is 

 shortly to be turned over to the National Physical Labora- 

 tory." This seems rather in want of explanation. 



A CORRESPONDENT asks where he could obtain a portable 

 and very sensitive instrument with which to measure the 

 acceleration of gravity. In reply to the inquiry, Dr. C. 

 Chree has been good enough to provide the following- 

 information : — " The determination of absolute values of g 

 (acceleration of gravity) with high precision is an attempt 

 verv rarelv made. For a good many years past relative 

 determinations have almost all been made with half-second 

 pendulums. The half-second pendulums originally obtained 

 for the Indian Survey, which were swung at Kew in 

 1903, are described in Major Lenox Conyngham's paper on 

 the subject (Roy. Soc. Proc, vol. Ixxviii., 1906, p. 241) as 

 ' made by E. Schneider, of Vienna, after Col. von 

 Sterneck's design.' He also says: 'The clock belonging 

 to the apparatus was constructed by Strasser and Rohde, of 

 Glashiitte ; its pendulum, made by Riefler, of Munich, is 

 of invar.' At the present moment Prof. Helmert, of 

 Potsdam, is considered the leading authority on the subject. 

 Of late years pendulums of invar have been tried at 

 Potsdam, as temperature uncertainties in the field are 

 amongst the most troublesome. The usual procedure is to^ 

 swing the pendulums at a base station — e.g. the observa>.| 

 tory at Potsdam — where g is supposed to be known, andj 

 thence to deduce its value at any other place where th« 

 pendulums are subsequently swung." 



Messrs. Cassell and Co., Ltd., have commenced al 

 reissue of Mr. W. F. Kirby's well-known " Butterflies- 

 and Moths of Europe," to be completed in thirty -two 

 weekly parts. Part i. appeared on May 25. 



The Admiralty has ordered from Messrs. Newton and 

 Co., of 3 Fleet Street, London, ten sets of X-ray apparatus 

 to be supplied to the new battleships for service afloat. 

 We understand that these will make altogether thirty 

 complete installations that this firm alone has recently 

 supplied to the ships of the Royal Navy. 



