January 31, 1895] 



NA TURE 



325 



them being General F. T. Lloyd, Mr. Jeremiah Head, Prof. 

 J. \V. Judd, Prof. Roberts-Austen, Mr. H. A. Wig^in, .Mr. E. 

 Matlhey, Prof. W. A. Tilden, Prof. A. \V. Riicker, Prof. G. 

 3. Howes, Mr. \V, Gowland, Dr. W. P. Wynne, Prof. C. V. 

 Boys, Prof. J. B. Farmer, and Prof. A. K. Hunlingdon. 



The following arrangements have been made for lectures at 

 the Royal Victoria Hall, Waterloo Bridge Road, S.E., during 

 February: Sir Colin Scott MoncriefT on "Egypt and the 

 Nile'' ; Mr. Smith Woodward on " -\ Visit, to Russia" ; Dr. 

 J. Norman Collii on " The Alps around Mont Blanc "; Prof. 

 Ramsay, F.R.S., on "Some New Discoveries about the Air." 

 This lecture will have special reference to the investigations 

 by Lord Rayleigh and Prof. Ramsay, which resulted in \\\t 

 discovery of a new constituent of the almoiphere. 



The twenty-first general meeting of the Association for the 

 Improvement of Geometrical Teaching was held at University 

 College on January 19, Dr. R. Wormell, the Presiilent, in the 

 chair. The report of the Council, prop )sing the continuation 

 of the Mathematical Gazette, and the Treasurer's report were 

 read and adopted. Dr. Larmor, of St. John's College, Cam- 

 bridge, was elected President in the place of Dr. Wormell, who 

 retires ; the other members of the Council, including, the hon. 

 sees., R. Holmes (The Avenue, St. Margaret's, Twickenha'n) 

 and C. Pendlebury (53 Gunterstone Road, West Kensington), 

 were re-elected. .Vfter the elections, Mr. E. iNL Langley gave 

 some geometrical notes, and Mr. G. E. Heppel read a paper on 

 " .\lgebra in Schools." .\fter an adjournment. Dr. Larmor 

 took the chair, and papers were read by Rev. C. Taylor (" The 

 A. \. G. T. Syllabus of Geometrical Conies ") and Rev. J. J. 

 Milne ("The Conies of .\pollonius"j, and Prof. Lodge gave 

 some notes on Mensuration. Interesting discussi ins followed 

 these. All communications with respect to the Mathematical 

 Gazette %\io\Ad, be addressed to the Editor, 16, Adelaide Square, 

 Bedford. 



Colonel A. T. Eraser, writing to us from Bagdad, says 

 that while travelling lately on the right bank of the Euphrates, 

 he noticed a pair of caves near the usual black woollen cloth 

 tent lived in by the -Vrabs, and found that, as evening drew in, 

 a number of cows were driven down, and the caves shui with 

 plugs of straw and thorns. " It was evident," he says, " that 

 this must have been the primary use to which those early types 

 of man of the dint and bronze ages, about whom we know so 

 little, put the so-called cave dwellings, that of sepulture being 

 an after- thought. Une would imagine, reasoning hastily, that 

 cows and .-Vrabs should have more properly changed places. 

 But the .Vrabs bring the experience of thousands of years to 

 bear on this question, and prefer the free air to a confined 

 atmosphere suitable only to ruminant beasts, and tents to caves. 

 Having alluvial soil to deal with, the Arabs in this instance dug 

 pits about four feet deep, and domed over the top with brush- 

 wooci and straw to compLte the caves, the whole showing but 

 little above the surface. There was no need of permanence, as 

 encampments shift with the seasons. Under other circumstances 

 the old " cave ' races would have dug the entire cavity out of 

 the solid, but still put in their cattle, and remain outside them- 

 selves." 



For some classes of observations involving the use of a 

 spectroscope, the movement of either collima'or or observing 

 telescope is objectionable, and for such work it becomes 

 necessary to rotate the prism in order to bring different parts 

 of the spectrum into the field of view. If the condition of 

 minimum deviation be of no importance, as in the case of Mr, 

 ' Tutton's apparatus for obtaining monochromatic illumination, 

 there is no objection to turning the prism in this way, but if 

 the condition of minimum deviation for the central ray in the 



NO. 15 18, VOL. 51] 



field is to be retained, some special device is essential. This 

 has already been accomplished in various more or less elaborate 

 ways, but Mr. F. L. O. Wad^worth has now indicated a means 

 of satisfying this condition very simply {Astronomy an i Astro- 

 physics, December 1894). The general solution of the problem 

 is effected by the introduction of a mirror into some pan of the 

 spectro-copic train between the slit and the focal plane of the 

 observing lens, the mirror having an angular movement equal 

 to one half the change in angular motion of the ray refracted 

 at minimum deviation. The mirror may be disposed in several 

 ways, but that finally adopted for use with the speclro-bolo- 

 meter is to place it in continuation of the back face of the 

 prism. With this arrangement the emergent ray is parallel to 

 the incident one, so that a direct vision spectroscope is obtained 

 by the use of a single prism. The prism and mirror are 

 together m lunted on the graduated circle of the spectrometer, 

 and by making the axis of rotation of the system coincident 

 with the intersection of the plane bisecting the refracting angle 

 of the prism and the plane of the mirror, there is no lateral 

 displacement of the ray at minimum deviation. The idea 

 seeiiH to be an excellent one, and capable of wide application. 



That gales have a considerable effect upon the heights of 

 tides is very well known. The gale of January 23, furnished 

 an example of this at the East India Dock, .\ccordiiig to a 

 letter in the Times, high water was due at the Dock at 

 I2'46 a.m. on January 24. At ten o'clock on the previous 

 evening, however, the tide had risen three inches above 

 Trinity datum, and then fell 5 feet 4 inches to midnight. 

 It again rose five inches to i a.m., when it went away 

 altogether. The phenomena suggest that, probably, the 

 records of self-registering tide gauges, when discussed 

 in connection with high winds and cyc'ones, will furnish 

 useful results. Prjf. Cleveland Abbe notes in the Monthly 

 Weatlitr Review that, during a hurricane at Charlest-jn last 

 September, the excess of the actual over the normal high water 

 mark increased gradually until it reached more thsn five feet. 

 I In this connection some observations on the indication of dis- 

 tant storms by tides are of interest. Captain E- Jones, who for 

 many years kept logs of deep-water voyages of Lieutenant 

 Maury, states that, previors to a cyclonic storm which 

 occurred early in September, he no. iced that at low water the 

 tide did not fall near as low as under ordinary conditions, and 

 he came to the conclusion that a cyclone was approaching, as 

 he had noticed before that under these conditions such storms 

 are very certain to mike their appearance. He testifies " that 

 this abnormal condition is an infallible indication of a storm 

 approaching or passing by. .-V storm directly in from seaward 

 generally affects the Hood tide even more than a low water 

 tide, but in the present case the high water was about normal. 

 A long experience gives me great confidence in the barometer 

 as affording valuable prognostication of a storm, but this tidal 

 wave along the coast preceding a cyclone must, as it seems to 

 me, give abioliue proof that some kind of storm is in progress ; 

 the astonishing thing is that the ocean level is aft'ected by the 

 cyclone at such a great distance, and especially ahead of it." 



In the American Engineer for January, Prof 11. A. Hazen 

 gives some of the results of a very interesting balloon ascent 

 made in the "Svea"at Stockholm, by S. A. Andree. The 

 account is taken from the Procceiiings of the Swedish .\cademy, 

 vol. 20, part ii. , No. 3. The balloon travelled for 136 miles east 

 over the Ualtic, the highest point reached being 9900 feet, and 

 at the time of the ascent, Stockholm was nearly in the centre of 

 a high barometric area ; this fact, in connection with the posi 

 tion of the balloon over a wide, expanse of water, adds great - 

 interest to the observations. The diminution of temperature 

 with height, allowing for increasing heat during the day, was 



