October 4, 1900] 



NATURE 



565 



the flame was in the same way independent of the conductivity 

 of the flame. 



At the close of the meeting of the section on Wednesday 

 morning, September 12, votes of thanks to the president and 

 secretaries were passed, and the section adjourned to Glasgow. 



C. H. Lees. 



ASTRONOMY AT THE BRITISH 

 ASSOCIA 7 ION. 

 A STRONOMY this year constituted a distinct department of 

 -^*- Section A, with its own chairman and secretaries, and a 

 separate room was provided for the reading of papers on this 

 subject. The new departure was sufficiently justified by the 

 attendance at the meetings, and in future years, when the 

 formation of the Department of Astronomy becomes more widely 

 known, increased success may be confidently expected. The 

 department met on Friday, September 7, and Tuesday, Sep- 

 tember II, and altogether sixteen papers were read. 



At Friday's meeting, after the chairman's address, three 

 papers by Prof. Todd, relating to eclipse work, were read by 

 one of the secretaries in the absence of the author. In one of 

 these attention was called to the " application of the electric 

 telegraph to the furtherance of eclipse research." In 1878, the 

 idea first occurred to Prof. Todd to telegraph eastward in 

 advance of the lunar shadow in order to enable the immediate 

 verification of any possible discovery, as of an intramercurian 

 planet, without waiting for another eclipse. The feasibility of 

 the method was demonstrated in January 1889, and again more 

 completely during the eclipse of May 28, 1900. At the station 

 occupied by Mr. Douglas in Georgia, totality preceded the same 

 phenomena in Tripoli, where Prof. Todd himself was observing, 

 by 2h. 45m., and the outcome of the experiment was that, 

 through the generous help afforded by the various telegraph 

 companies, an account of the American observations was received 

 by Prof Todd more than two hours before totality occurred at 

 Tripoli. Abundant time for special preparations to verify any 

 important discovery was thus available. 



In his second paper Prof. Todd dealt with a variety of 

 methods of operating eclipse instruments automatically. The 

 " mechanical system," as distinct from the pneumatic and 

 electric arrangements which he had previously devised, was first 

 tried during the recent eclipse. The instruments being set up 

 on the roof of the British Consulate, gravity was utilised for the 

 mechanical operation of slides and shutters. One hundred 

 photographs were secured at Tripoli by seven instruments 

 operated in this manner. Experience indicates that the gravity 

 method is the best where the number of instruments is not 

 great. 



Another paper by Prof. Todd described the use of a wedge 

 of yellow optical glass in giving correctly graduated exposures 

 of the partial phases and corona on a single biograph film. 



An important paper on the classification of sun-spots was 

 read by the Rev. A. L. Corti, S.J., and illustrated by a fine 

 series of lantern slides selected from the thousands of drawings 

 made at Stonyhurst during the last twenty years. Five types, 

 with a certain number of sub-divisions, were found sufficient to 

 denote the characters of all the spots which had so far been 

 examined. 



The chief type, of which the others are probably but phases, is 

 the two-spot formation. The faculne associated with the dif- 

 ferent types are also of diff'erent characters, and it may be pos- 

 sible to foretell the outburst of a spot by the observation of a 

 certain kind of facuJa. As an illustration of the use of the type 

 numbers, the life-history of a composite disturbance which 

 cros.sed the solar disc five times between May 14 and September 

 4, 1887, was thus described : — 



I., 11.6 I IV.^, IV.a I IV.a, IW.d, IW.a \ IV.a, I., Il.a | I. 



In the course of the discussion on this paper it became evident 

 that the need for some short system of notation had long been 

 felt by observers of sun-spots, and that, providing the scheme 

 suggested would cover all cases, it would be very valuable. The 

 chairman remarked that possibly a still better system, which 

 would tax the memory less, might be devised on the plan of 

 Herschel's notation for nebulae. 



Prof. Turner exhibited and explained " a cheap form of 

 micrometer for determining star positions on photographic 



NO. 1 6 14, VOL. 62] 



plates." The essential features are a wooden frame to support 

 the photograph, with an attachment carrying a simple micro- 

 scope containing a scale in the eye-piece. For less than thirty 

 shillings an efficient instrument can be constructed, capable of 

 yielding measures of practical utility. It thus becomes possible 

 for any one to undertake important researches at a much smaller 

 outlay than would be involved in the purchase of a telescope, 

 since there is no lack of material to work upon. Among the 

 investigations mentioned by Prof. Turner as possible with such 

 a machine, were the determination of the positions of nebulae 

 and comets, and measurements to ascertain the forms of the 

 trails of meteors. Considerable interest in the proposal was 

 displayed, and the hope was expressed that many who now 

 spend their time in fruitless star gazing with small instruments 

 may be induced to undertake these micrometric measurements. 



Thursday's meeting was opened with an interesting paper by 

 Dr. Lockyer, in which a comparison was made of the details of 

 the prominences and corona as shown in photographs taken 

 during the recent eclipse at intervals of 2^ hours, by Prof 

 Langley and Sir Norman Lockyer, in America and Spiin 

 respectively. While enormous changes in the prominences were 

 revealed, no change was detected in the structure of the corona 

 in the region of the North Pole, which had been specially 

 investigated. An interesting feature of one of the photographs 

 taken in Spain with an exposure of 40 seconds was the extreme 

 hardness of the moon's limb, notwithstanding the relative 

 motion of the moon during the exposure ; the explanation of 

 this unexpected appearance was based on the rapid diminution 

 in intensity of the corona as the outer layers are reached, so that 

 the momentary exposures of the lower corona on the advancing 

 limb of the moon at the beginning of the exposure, and on the 

 following limb at the end, were sufficient to give a strong 

 impression. 



The new form of refracting telescope recently erected at. 

 Cambridge, chiefly for photographic work, was described by 

 Mr. A. R. Hinks, and illustrated by lantern slides. The object- 

 glass is a Taylor triple lens of 12^ inches aperture, and the chief 

 peculiarity of the mounting is that the portion which is usually 

 the lower half of the tube forms the polar axis, Avith the eyeend, 

 at the top, while the object-glass end is hinged to the other 

 piece, and a plane mirror is placed at the junction. In another 

 paper Mr. Hinks referred to the preparations which are being 

 made for determining the solar parallax by observations of Eros 

 during the coming winter, and exhibited a series of diagrams 

 showing the path of the Cambridge Observatory as seen from 

 that planet at various times. With the aid of such diagrams 

 the observer can see at a glance the most favourable times for 

 making micrometric measurements or taking photographs for 

 the purpose in hand. The importance of the observations of 

 Eros was emphasised by Prof. Turner, who remarked that at 

 the present time the probable error of the adopted value of the 

 .solar parallax was equivalent to the thickness of a wicket in the 

 length of a cricket pitch. Unlike the transit of Venus, the 

 observations of Eros would be easily reduced, and the results of 

 the observations would soon be accessible. 



A paper on " some points in connection with the photography 

 of a moving object, ' by Mr. W. E. Plummer, had an important 

 bearing on the photographic method of ascertaining the position- 

 of such a rapidly moving object as the planet Eros. A com- 

 parison of measurements of the positions of a comet made with 

 a micrometer and those determined from photo^jraphs indicated 

 that considerable errors might be introduced in the photographic 

 results on account of the difficulty of determining the epoch of 

 observation. Since the first few moments of exposure on the 

 moving object leave no impression, the middle of the trail does 

 not correspond to the middle of the exposure. In exposures of 

 ten minutes on Eros the danger of error was very con.siderable. 

 Mr. Hinks remarked that it was hoped to obtain sufficiently 

 strong impressions of the field containing Eros with exposures 

 of one or two minutes, under favourable circumstances, and, 

 moreover, special precautions to eliminate this difficulty had 

 been arranged at the Paris Conference. 



Mr. John Herschel described in detail his method of observing 

 and recording the paths of meteors. Special maps are con- 

 structed in which the brighter stars are represented by perfora- 

 tions made with needles of various sizes, the side of the paper 

 away fiom the observer being blue, while that towards him is 

 white. The map being laid on a sloping desk of ground glass 

 illuminated by a night light, the paths of the meteors are ruled 

 in by means of a transparent celluloid ruler having a black edge. 



