250 



NATURE 



[July 15, 1897 



brightness in each 6-hour interval of the period was 

 set down for each group, together with the correspond- 

 ing time and the number of observations. In this 

 way the whole of the materials collected by Schmidt 

 from 1844 to 1879, and thus covering eighteen groups of 

 100 periods each, are expressed in tabular form on p. 21 

 of Dr. Lockyer's dissertation. The numbers for each 

 period were then plotted on millimetre paper ; tentative 

 and afterwards definite curves representing the fluctua- 

 tions of the star's light were drawn through the points 

 thus obtained. The resulting eighteen curves represent- 

 ing Schmidt's observations are reproduced one above the 

 other on a small but distinct scale on Plate I., each curve 

 being prolonged by about one-third of the period to 

 bring out the form of the minimum. A study of these 

 curves shows that Argelander's period cannot, at present, 

 be improved on as a mean value. The time of Arge- 

 lander's epoch 400 is, however, shown to be too early by 

 an interval which the author fixes at 3'2655 hours. The 

 curves also show conclusively that the epoch of maximum 

 oscillates to and fro to the extent of five hours on either 

 side with a period comprising 400 maxima. In the same 

 way the minima are subject to an oscillation of about 

 three hours in approximately 2400 periods. The com- 

 bined effect of these variations causes the light-period to 

 vary between 7d. 4h. 14m. 40s. and 7d. 4h. 13m. 28s. 

 also in 2400 periods. Superposed on the main light 

 curve are four subordinate undulations, of which more 

 hereafter. 



Much the same method was followed with regard to 

 the observations of Argelander, Schonfeld, Heis, Plass- 

 mann, Oudemans, Pannekock, Auwers, Knopf, Sawyer 

 and Schur ; but with the further step of reducing the 

 estimated grades to Argelander's scale. This reduction, 

 carried out with scrupulous care by the method of least 

 squares, brings out several interesting facts regarding 

 the values which the grade, or unit of brightness, assumes 

 in the case of the different observers, or for the same 

 observer at different times. Here there is only space to 

 mention the observations made by Knopf in Jena. Con- 

 trary to the general usage of comparing a variable with 

 stars differing from it in brightness by at most five or six 

 grades, Ur. Knopf often allowed himself a range of no 

 less than nineteen grades. This new departure has most 

 unexpectedly had no injurious effect on the accuracy of 

 the observations, as is abundantly proved by the small- 

 ness of the residuals in the evaluation of the brightness of 

 the comparison stars. From the materials collected by 

 the observers just named, the author constructed nine- 

 teen further curves, which confirm in a high degree the 

 results from Schmidt's observations alone. Dr. Lockyer 

 also tests the accuracy of his conclusions by means of 

 the long series of observations made by Wurm in the 

 course of twenty-seven years, beginning with 1785. The 

 detail, indeed, of these observations seems never to have 

 been published, but the actual length of the period in 

 accordance with Schmidt, for the epoch of Wurm's 

 observations, differs but seven seconds from Wurm's 

 value ; and since the early observations also show de- 

 cided indications of the oscillation of the time of maximum, 

 it seems certain that the general character of the vari- 

 ability of 17 Aquila; has not materially changed in the 

 course of the last hundred years. 



As regards the four secondary fluctuations, they are 

 found to recur at intervals of forty-three hours, or one 

 quarter of the main period, the first of these secondary 

 maxima occurring fifteen hours after the chief minimum. 

 The author is the first to have clearly brought out this 

 feature, and he explains it by assuming, in accordance 

 with his father's hypothesis, that the system of r\ Aquilas 

 consists of three meteoric swarms, of which the two 

 lesser revolve about the greater m periods of id. igh. -f 

 .and 7d.4h.-l- respectively (see " Meteoritic Hypothesis," 



NO. 1446, VOL. 56] 



passim, but particularly pp. 475-6), The irregularities 

 in these fluctuations are set down to the perturbations 

 necessarily occurring in such a system, but their in- 

 vestigation did not come within the scope of the essay 

 before us. Figs, i and 2 of the dissertation show the 

 proportions of the assumed orbits, together with the 

 form of the light curve resulting from the combination 

 of the two elementary curves. In conclusion, I must 

 express my admiration of the skill and untiring per- 

 severance which Dr. Lockyer has shown in dealing with 

 a large mass of somewhat intractable material. 

 Wherever possible the deductions were made from the 

 original manuscripts, concerning which interesting par- 

 ticulars are given on pp. ig and 20, where we learn that 

 Schmidt's original notes are preserved at Potsdani, 

 while those of Heis have wandered across the Atlantic 

 to the observatory of Georgetown College. 



R. COPELAND. 



BRITISH ASSOCIATION TORONTO MEETING. 

 III. Local Arrangements. 



THE two leading Hydraulic Companies of Niagara 

 Falls are making special arrangements for the 

 reception of the members of the British Association. 



The Carborundum Company of Niagara Falls has 

 extended an invitation to the members of the Association 

 to visit and inspect the Company's works on Saturday, 

 August 21. The manufacture of carborundum by this 

 Company has been fully described in Nature for May 13 

 (p. 42). 



The Atlantic Cable Companies have generously 

 arranged that members from Great Britain may send 

 two free cable messages from Toronto, and they will then 

 be entitled to two free replies. Each message and reply 

 are not to contain more than ten words each, and they 

 are to be forwarded by agents recognised by the Cable 

 Companies. The agents in Great Britain will, in all 

 probability, be Messrs. Cook and Son, and in Toronto 

 the Honorary Local Secretaries ; but the arrangements 

 in regard to this are not complete, and a fuller announce- 

 ment will be made later. It is to be noted that the 

 transmission of the messages within Great Britain to 

 and from the head office of Cook and Son will be 

 charged for as ordinary telegraphic messages. The 

 arrangements in this respect are the same as those made 

 in 1884. 



In order to avoid delay in the Customs examination of 

 the members' luggage, the Hon. Mr. Paterson, the 

 Minister of Customs, has given special instructions to 

 the Customs officers at Quebec, Montreal and Niagara to 

 facilitate in every way the examination. A larger number 

 of examining officers will be on duty at Quebec, and 

 one will accompany each steamer from Quebec to 

 Montreal to make the examination of the luggage during 

 the passage. As a result of this arrangement, all delay 

 at Quebec and Montreal will be avoided. The Minister 

 of Customs has also arranged that all scientific apparatus 

 or material for use during the meeting of the Association 

 shall be admitted free of duty if forwarded to me at 

 Toronto, and marked, " For British Association." 



It is expected that there will be in attendance at 

 Toronto more than twenty continental men of science of 

 a representative character. Amongst those who have 

 intimated their intention to be present are Prof. Charles 

 Richet, Prof Yves Delage, both of Paris ; Prof Meslans, 

 University of Nancy ; Prof Gilson, of Louvain ; Dr. van 

 Rijckevorsel, of Amsterdam ; Dr. Pauli, of Frankfort ; 

 Prof Ladenburg, of Breslau ; Prof Runge, of Hanover ; 

 Prof Brauner, of Prag ; Prof Penck, of Vienna ; M. 

 Letourneau, of Paris ; M. Gobert, of Brussels ; and Prof. 

 P. Magnus, of Berlin. « A. B. M.^CALLUM. 



