564 



NATURE 



{April, II, 1889 



sufficient grounds for regarding the Hatteriidcc, with the 

 single genus Sphenodon, as a different family. 



Dr. Credner's paper also contains, incidentally, informa- 

 tion on Proterosaurus, the structure of which is still, in 

 spite of Prof. Seeley's recent investigations, very imper- 

 fectly known. In an example preserved in Freiberg, the 

 author has discovered the interclavicle and clavicles, the 

 former element closely resembling the same in Palao- 

 hatteria, whilst the latter is distinguished by its plate-like 

 proximal expansion, which bears special resemblance to 

 the so-called lateral pectoral plates of certain Stego- 

 cephalians. It appears almost certain that Froterosaurus 

 was a Rhynchocephalian, but in many respects more 

 specialized than Palaohatteria, intercentra being present 

 only between the anterior cervical vertebrae, and the 

 tarsus containing only six elements — three in the proximal 

 and three in the distal row. G. A. Boulenger. 



THE SPECTRUM OF THE RINGS OF SATURN. 

 A N interesting note on the spectrum of Saturn's rings 

 ■^"^ was communicated to the Royal Society on Feb- 

 ruary 7 by Mr. Norman Lockyer. It has long been 

 known that the rings are considerably more luminous 

 than the planet, and the photographs by the Brothers 

 Henry show that this is truer for the blue light than the 

 more visible rays. It is therefore possible that they 

 shine partly by their own light, and since it is now uni- 

 versally acknowledged that they consist of small bodies 

 in motion, their spectrum has an important bearing on 

 the meteoric hypothesis. Mr. Lockyer suggested that 

 the additional luminosity might be due to collisions, and 

 in order to determine whether the collisions were of suffi- 

 cient intensity to produce incandescent vapours or not, 

 he asked one of his assistants, Mr. Porter, to obtain a 

 photograph of the spectrum. This was done at the 

 Astronomical Laboratory at South Kensington, with a 

 spectroscope having two prisms of 60° attached to the 

 eye-end of the lo-inch equatorial. The photograph was 

 taken with an exposure of about two hours, and shows 

 decided indications of bright lines. Mr. Lockyer says : — 

 " It is altogether too early to announce this as an esta- 

 blished fact, but I think it well to send this note, in order 

 that other observers with more powerful optical appli- 

 ances and a better climate than that of London may 

 investigate the question." 



It is therefore very desirable that further inquiry should 

 be made, both by photographic and eye observations. 

 The bright flutings of carbon at wave-lengths 517, 474, 

 and 564 should receive particular attention, the flutings 

 being easily obtained for comparison from the flame of a 

 spirit-lamp or wax vesta. Brightnesses may possibly 

 occur also in the positions of the magnesium flutings at 

 X 500 and 521, the lead fluting at X 546, and the man- 

 ganese fluting at X 558, all of which may be conveniently 

 obtained for comparison by volatilizing the chlorides of 

 these substances in the flame of a spirit-lamp or Bunsen 

 burner. 



It may be expected that the brightenings will be very 

 feeble, owing to the masking effects of the more abundant 

 solar light, so that the photographic method will probably 

 give the best results on account of its power of 

 integration. 



In the same note, Mr. Lockyer states that "other con- 

 siderations point to the possibility that bright lines or bands 

 may be found in the spectrum of Uranus." A. F. 



ON THE SPEED OF THE ELECTRIC 

 TRANSMISSION OF SIGNALS THROUGH SUB- 

 MARINE CABLES AND LAND WIRES. 

 "PLECTRO-TELEGRAPHIC operations for the de- 

 ^-^ termination of differences of longitude are usually 

 so arranged as to furnish determinations of the speed of 

 transmission of the electric signals. Each of two sta- 

 tions which are telegraphically connected is provided 



with a clock, and usually with a chronograph also ; thus 

 the clock-times at either station may be registered at 

 will on the chronographs at both stations. The difference 

 between the times indicated by the two clocks at any 

 moment is thus readily ascertained, and two values of it 

 will be obtained, one with the current transmitted in one 

 direction, the other with it transmitted in the opposite 

 direction. The difference between these two values indi- 

 cates the sum of the speeds in both directions ; and half 

 the difference is usually called the " retardation on the 

 line," as it indicates the amount by which every signal, on 

 arrival at its destination, is slow on the time of its 

 inception. 



This method of determining the velocity is very simple 

 and very exact ; it does not require a knowledge of the 

 errors of the clocks, or even of their rates, for the rates 

 cannot sensibly alter in the brief interval between the 

 signals with reversed currents, which need never exceed 

 a few minutes. 



The operations of two officers of the Indian Survey, 

 Lieut.-Colonel Campbell, R.E., and Major Heaviside, 

 R.E., for determining the differences of longitude between 

 Bombay, Suez, and Aden,^ furnish measures of the speed 

 through two submarine cables which happen to be prac- 

 tically identical, though one cable was 355 knots, or as 

 much as one-fourth, longer than the other cable. I gave 

 the figures to Mr. W. H. Preece, of the Postal Telegraph 

 Department, and he has found that they are very closely 

 accordant with the theoretical speeds, calculated with due 

 recognition of the different electrical conditions of the 

 two cables. This is shown in the following table, in which 

 Mr. Preece also gives the corresponding values by calcula- 

 tion and observation for the French Atlantic cable : — 



Suez-Aden 

 Aden- Bombay ... 

 French Atlantic, 



17 X KR 

 I per knot. 



3-67 7865162 



2-381787485 

 1-268413090 



sec. 

 •280 



•284 



•3 



For the speed of electric transmission through land 

 lines, German geodesists have constructed an empirical 

 formula on the assumption that the speed = xl -f- yP, 

 I being the length of the line, and x and/ two constants 

 to be determined by observation. It is shown in the 

 Astronomische-geoddtische Arbeiten for the years 1883- 

 84 and 1885-86, that, expressing / in kilometres, 



the speed = o-oooo2o8s. / + o-ooooooo2o6s. /^ 

 on the evidence of seventeen longitudinal arcs ; and that on 

 employing this formula to calculate the corresponding 

 speeds in six arcs subsequently measured, the values ob- 

 tained were found to differ 38 per cent, on the average from 

 the observed speeds, and were generally quicker. This 

 formula, however, takes no account of any differences 

 in the electrical conditions of the lines. It gives o-2o6s. 

 and 0-302S. as the speeds of transmission through land 

 lines 2700 and 3360 kilometres long, the lengths of the 

 cables Suez-Aden and Aden-Bombay. The formula, 

 however, cannot be legitimately applied to such long 

 lines, for the longest of the seventeen on which the 

 speeds were determined by observation, that from Berlin 

 to Paris, was only 1230 kilometres. ]■ T. Walker. 



13 Cromwell Road, London, April 3. 



' See vol. ix. of the "Account of the Operations of the Great Trigono- 

 metrical Purvey of India." (Dehra Dun, 1883.) 



