562 



NA TURE 



[Oct. 13, 1887 



NEW FORM OF CONSTIWCriON OF OBJECT- 

 GLASSES INTENDED FOR STELLAR 

 PHOTOGRAPHY. 



THE interest now generally taken in stellar photo- 

 graphy will probably make it desirable that the 

 object-glasses of telescopes ordinarily used for visual pur- 

 poses should be so constructed as to be readily adapted 

 to photographic use. ' As now commonly made, the cor- 

 rection for chromatic aberration by means of the flint- 

 glass lens of a refracting telescope is too great to give 

 satisfactory photographic images. The method of adapt- 

 ing such a telescope to photographic purposes which was 

 employed by Mr. Rutherford, and more recently in the 

 case of the great telescope of the Lick Observatory, is to 

 provide an additional convex lens of long focus which 

 may be mounted when photographs are to be taken, and 

 removed when direct observation is desired. The objec- 

 tions to this method are the expense of the additional 

 lens and the introduction of two more surfaces. 



Another way of removing the excessive correction for 

 chromatic aberration is to separate the flint- and crown- 

 glass lenses, and to place the flint nearer the eye- piece. 

 But when this is done, while the correction for colour 

 becomes satisfactory, the spherical aberration is only 

 partially corrected, the focal length of the central part of 

 the object-glass being greater than that of the surround- 

 ing portions. This difficulty, however, may be sur- 

 mounted by giving different curves to the two surfaces of 

 the crown-glass lens, and reversing it when the lenses are 

 separated. 



In an object-glass of this construction, when used for 

 direct observation, the two lenses are in contact, with the 

 more convex side of the crown lens next the flint. For 

 photographic use, the lenses are separated, and the more 

 convex side of the crown-glass lens is turned outwards. 

 In order to determine whether this principle of construc- 

 tion should be adopted in the case of a large object-glass 

 to be made for experimental work undertaken with the 

 aid of the Boyden Fund, recently transferred to the 

 Observatory of Harvard College, for the purpose of ob- 

 taining astronomical observations at elevated stations, a 

 small object-glass was made upon the new plan by 

 Messrs. Alvan Clark and Sons. As this object-glass 

 proved to be well adapted to its purpose, the larger 

 object-glass above mentioned has been similarly con- 

 structed by the same makers; its aperture is 13 inches, 

 and its focal length about 180 inches. Upon trial, it is 

 found that the images formed by this object-glass are 

 excellent when the instrument is used for direct observa- 

 tion, and that the photographic images are equally good 

 when the lenses are separated 3 inches and the crown- 

 glass reversed. 



The curvature given to the surfaces of such an object- 

 glass will depend upon the quality of the glass employed ; 

 in this particular instrument the radius of curvature for 

 the less convex side of the crown-glass is 86 inches ; for 

 the more convex side, T"] inches ; for the concave side of 

 the flint, 73"8 inches ; the side of the flint-glass which is 

 turned towards the eye-piece is convex, and its radius of 

 curvature is 1020 inches. 



Edward C. Pickering. 



Harvard College Observatory, Cambridge, U.S., 

 September 29. 



WILLIAM S. SYMONDS. 



V\/E have already announced the death, on September 

 ^^ 1 5, at Cheltenham, of the Rev. William S. Symonds, 

 Rector of Pendock, F.G.S., and a J. P. for the county of 

 Worcestershire. Mr. Symonds, the eldest son of Mr. 

 William Symonds, of Elsdon, Hereford, was born in Here- 

 ford in 1 81 8, took his degree at Christ's College, Cam- 



bridge, in 1842, and in 1868 was presented to the Rectory 

 of Pendock. 



For several years past Mr. Symonds had suffered from 

 heart-disease, and was compelled to withdraw from his 

 parish duties, as well as from participation in those scien- 

 tific pursuits in which he had long been actively occupied. 



The intimate friend of Murchison, Lyell, and of other 

 pioneers in geology, and frequently their companion in 

 their excursions, he enjoyed exceptional opportunities for 

 observing the facts relating to this science, and has con- 

 tributed numerous papers, chiefly on the rocks and fossils 

 of the west of England, to the scientific periodicals. Yet 

 he sometimes engaged in discussions of a more general 

 character. In the question of the reptiliferous sand- 

 stone of Elgin he took much interest. Before the meet- 

 ing of the British Association at Aberdeen, in 1859, he 

 visited the Elgin area, and, having worked over it with 

 great care, was led to accept the views of Sir C. Lyell in 

 opposition to those of Murchison ; and in the discussions 

 at the meeting strongly insisted on the view that the 

 reptiliferous sandstones are of the New Red or Triassic,. 

 and not of the Old Red Sandstone age. 



Mr. Symonds did not devote as much attention to 

 palaeontology as to physical geology, although even in 

 this branch of the science he has left his mark, and has 

 made numerous and valuable contributions from his 

 collections of fossils to several local museums. 



During the latter part of his life his interest was much 

 concentrated on the phenomena of the glacial drifts, and 

 the question of the antiquity of prehistoric man. In 1871 

 he communicated to the Geolo^^ical Magazine (p. 433) a 

 paper on the great Doward Caves, and in his " Severn 

 Straits, or, Notes on Glacial Drifts," he gives his con- 

 clusions on this subject. 



But it is perhaps chiefly as an earnest and eloquent 

 expounder of the facts and principles of geology and 

 cognate subjects that he will be remembered. He had a 

 remarkable power of infusing his own spirit of research 

 and love of Nature into his writings. Few can read his 

 " Records of the Rocks," " Old Stones," and " Old 

 Bones," or his delightful romances of " Malvern Chase"' 

 and "Hornby Castle"— tales of the W^ars of the Roses 

 and the Parliament — without recognizing this. In the 

 formation and management of many of the field clubs 

 of the west of England Mr. Symonds's ability was espe- 

 cially conspicuous. He was engaged, with the late Mr. 

 Scobie, of Hereford, in the formation of the Woolhope 

 Field Club, and was elected its President in 1854. He 

 was the frequent companion of the late Sir William 

 Covin in his travels, and took an active part in the 

 management of the Cottesvvold Club, of which Sir 

 William was President. 



By those who had the privilege of an intimate acquaint- 

 ance with Mr. Symonds, he will ever be thought of and re- 

 spected as an earnest and most uncompromising seeker 

 after truth for its own sake. He considered that man is 

 performing a most religious duty when he sits as a humble 

 student at the feet of Nature to learn, as far as may be, 

 the lessons which Nature's Creator would teach him. It 

 was a faith, too, which, throughout the trying and painful 

 complaint that clouded the last days of his life, never 

 failed him, and which enabled him to look forward to, 

 and speak of, the great change which was before him, 

 with cheerful hope. 



The number of papers which Mr. Symonds has from 

 time to time contributed to various scientific journals 

 appears to have been over forty. 



NOTES. 



We reprint to-day from the Times an admirable letter by Mr. 



Samuel Smith on education in Germany. Mr. Smith gives a 



clear account of some important elemenvS of the educational 



system which the Germans are gradually bringing to perfection ; 



