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76 



NA TURE 



[September 23, 1909 



Few present-day engineers are aware that Watt pro- 

 iduced a steam tilt liammer some years before Nasmyth 



designed the type of hammer that bears his name. The 



works at Soho held at one time a great reputation for 

 •coppersmith work, and this class of work was done with 



a Watt tilt hammer, which continued to be in use until 

 .quite recently. A photograph of the hammer, together 

 •with many others showing machines used by Boulton and 



Watt, appears in an article in the Engineer for Sep- 

 rtember lo. In examining the illustration of one of the 



Soho boring machines, we are reminded of Watt's early 

 'troubles in boring his cylinders — on one occasion we find 

 'him rejoicing over a finished cylinder which was nowhere 



more than |-inch from true circularity. We agree with 

 ■ our contemporary that it is greatly to be deplored that the 



history of machine tools has not been preserved. The 



ingenuity which has produced the development of machine 

 'tools has contributed in no small degree to the rise and 



progress of mechanical engineering. 



A CONSIDERABLE extension of our knowledge of the elec- 

 ■trical strength of air has been made by Mr. E. A. Watson, 



of the University of Liverpool, who has measured the 



potential difference necessary to cause a spark to pass 

 •between two small metal spheres at various distances apart 



in air at pressures between one and fifteen atmospheres. 



His paper, and the discussion which arose on it, will be 



found in the .-Vugust number of the Journal of the Institu- 

 •tion of Electrical Engineers. From it we gather that air 

 ■compressed to fifteen atmospheres will stand an electrical 



stress of 40,000 volts per millimetre, and it is to be hoped 

 'that this fact will soon find its application in apparatus 



in which high insulation is required. 



Erratum. — In N.\ture of September 16, p. 339, second 

 • column, line twenty-two from bottom, the word satis- 

 factory should be unsatisfactory. The sentence should 

 read : — " With a sextant and artificial horizon, a low alti- 

 itude, such as 10° or 11° or below, is very unsatisfactory." 



OUR ASTRONOMICAL COLUMN. 



Hallev's Comet. — From a Central News telegram pub- 

 .lished in Monday's Daily Telegraph, we learn that Prof. 

 Burnham has obtained two photographs of Halley's comet, 

 with instruments at Yerkes Observatory. 



Observations of Perrine's Comet, igogb. — A further 

 • observation of Perrine's comet, made by Dr. Max Wolf 

 on September 5, is recorded in No. 4355 of the Astrono- 

 mische Nachrichten (p. 179, September 12). With the re- 

 flector, and a power of 140, the comet appeared as a 

 round, nebulous mass, of about 10' diameter, increasing 

 in intensity towards the centre. The brightness of the 

 whole comet is about equal to the fourteenth magnitude, 

 while the nucleus is about equal to a star of that magni- 

 'tude. 



Dr. Ebell gives an ephemeris for this comet in the same 

 journal showing that it should become about 1-5 magni- 

 tudes brighter than it is at present by October 17. The 

 observation of September 5 shows that this ephemeris then 

 required corrections of — im. 39s. and —23'. 



Observations of Mars. — In No. 4354 of the Astrono- 

 mische Nachrichten (p. 159) M. Jonckheere gives a draw- 

 ing illustrating his observation of August n-12. The 

 peculiar interest of the observation was the aspect of the 

 Novissima Thyle, which, although still covered with ice, 

 was detached from the polar cap. This feature of the 

 Martian landscape appeared oval, with its broad extremity 

 in long. 330° and its narrow end in long. 310'', its apparent 

 length being 1.42". 



_ Measures of the polar cap show that its apparent 

 ■diameter decreased from 4.33" on Julv i6 to 3-00' on 

 August 21. 



NO. 2082, VOL. 81] 



Further changes are recorded by M. Jarry Desloges in 

 No. 4355 of the same journal. Observations made with a 

 37-cm. refractor on the Revard plateau on September 3 

 showed that the white polar spot was divided completely 

 by a crevasse and a greyish region in long. 80°. The 

 region of the Lacus Solis and d'.\uror« Sinus,, so pale 

 during the previous rotations, showed considerable changes, 

 the details now appearing very different in form, colour- 

 ing, and position to what they did in 1907. Juventje Fons 

 is dark and easily visible, and the canal Coprates appears 

 to have changed its position since 1907. Nectar is dark 

 and broad, and .^ra.xes is double and very complicated in 

 its structure. Lacus Phoenicis is blackish and is doubled, 

 the southern portion being the smaller. Lacus Tithonius 

 has very indefinite edges, and two dark spots are seen 

 within its area. The Solis Lacus presents a number of 

 detailed features, and is much elongated in the direction 

 east-west. A number of canals, single and double, were 

 observed, and all the regions observed presented such a 

 complicated structure that it was found impossible to make 

 complete drawings. 



W.WER Vapour in the Martian .'\tmosphere. — Accord- 

 ing to a despatch published in the Times of September 17, 

 spectrograms of Mars and the moon, secured by a party 

 of Lick observers on the summit of Mount Whitney, 

 indicate that there is no appreciable quantity of water 

 vapour in the Martian atmosphere. Prof. Campbell sug- 

 gests that the positive results obtained by Prof. Lowell 

 and other observers may be attributable to water vapour 

 in the earth's atmosphere, but further details should be 

 awaited ere the recent negative results are accepted as 

 final. Tlie photographs are stated to have been taken 

 when Mars and the moon were at the same altitude, and 

 under similar conditions of the earth's atmosphere, yet 

 the vapour bands in the Martian are no stronger than in 

 the lunar spectra ; hence it follows that, at the time the 

 spectra were obtained, the quantity of water vapour on 

 Mars was apparently no greater than that on the moon- 



The AL-vximum of Mira in October, 190S. — Dr. Nijland's 

 observations of the magnitude of Mira, made at the 

 Utrecht Observatory during the period July, 190S, to 

 February, 1909, showed that the maximum (mag. = 3.5) 

 occurred on October 6, 190S (J.D. 241S221), five days 

 before the time given by Guthnick's ephemeris (Astrono- 

 mische Nachrichten, No. 4355, p. 165). 



The Spectroheliograph of the Catania Observ.atory. 

 — In an extract from vol. xvii. of the Rendiconti delta 

 R. Accademia dei Lincei, Prof. Ricc6 describes the spectro- 

 heliograph now in use at the Catania Observatory, the 

 first to be erected in Italy. 



The instrument is made to attach to a telescope, and 

 may be used with a prismatic, or a grating, dispersion. 

 The regulation of the transit of the primary slit across 

 the solar image is effected by a clepsydra containing water 

 with 20 per cent, of glycerine added. The diameter of the 

 solar image operated upon is 52 mm., but the primary 

 slit is but 37 mm. long, therefore the whole disc takes 

 two exposures. Some of the results obtained at Catania, 

 in 1908, are reproduced with the paper, which is also 

 printed in No. 8, vol. xxxviii., of the Memorie delta 

 Societa degli Spettroscopisti Italiani. 



Ha Images on Spectroheliograms. — In concluding a 

 letter to the Observatory, M. Deslandres states that, on 

 spectroheliograms taken in Ho light at Meudon, he has, 

 this year, noted numerous instances where the spectro- 

 register of velocities has revealed some very large radial 

 displacements, similar to those observed by Young in 1872 

 and Hale in 1892. These were thought to be exceptional 

 phenomena, but Mr. Buss, who calls them " horns," 

 claims that he has seen them with relative frequency. The 

 Meudon observations now confirm Mr. Buss's ocular 

 observations. 



Double-star Measures. — In Nos. 4353-4 of the Astro- 

 nomische Nachrichten, Prof. Burnham continues the record 

 of the observations of double stars made since the pubU- 

 cation of his General Catalogue. The majority of measures 

 refer to doubles otherwise neglected, and comparatively 

 few of the 2 or 02 are considered to require present 

 attention. About 150 systems are included in the list of 

 measures now published. 



