November ii, 1909] 



NA rURE 



47 



G.M.r. From this we see that the nearest approach to 

 the earth should occur on May 20, the distance then being 

 143 milMon miles. The revised elements indicate that the 

 comet should transit the sun's disc on May i8d. I4h., but 

 the transit will, of course, be invisible in Europe. It 

 appears possible that, at that time, the comet's tail may 

 extend beyond the earth and be visible in the midnight sky. 



From observations made with the 40-inch Yerkes tele- 

 scope Prof. Barnard concludes that the comet is brightening 

 rapidly, and was not fainter than magnitude 13-5 on 

 October 17-19; the diameter was estimated at 15", the 

 comet being a little brighter towards the centre. 



The Astronomischen Gesellschaft prize has now been 

 definitely awarded {AsUonomische Nachrichten, No. 4366) 

 to Messrs. Cowell and Crommelin. 



Saturn. — A telegram from the Flagstaff Observatory 

 announces that the lacings crossing Saturn's equatorial 

 bright belt, detected at that observatory, have now been 

 photographed there (Circular No. 114, Kiel Centralstelle). 



Mercury. — From the careful study of some twenty photo- 

 graphs, taken at the Massegros Observatory during the 

 elongation of September last, M. Jarry-Desloges arrives at 

 tile conclusion that the rotation period of Mercury coincides 

 with the perioa of revolution. The photographs show a 

 number of details {Astronomische Nachrichten, No. 4360, 

 p. 375, November ij. 



The " Flash " Spectru.m without an Eclipse. — Yet 

 another important development in solar spectroscopy 

 emanates from Mount Wilson, Messrs. Hale and Adams, 

 in No. 3, vol. XXX., of the Astrophysical Journal, describing 

 the apparatus and method whereby they have succeeded in 

 photographing the bright-line spectrum of the lower 

 chromosphere without waiting for a total eclipse. With 

 their apparatus such photographs may now be obtained at 

 ;iny time when the sun is observable. 



.\fter describing the previous attempts to attain this end, 

 made at Kenwood, Yerkes, and Meudon, they give a brief 

 description of the additions to the 30-foot spectrograph 

 which enabled them to accomplish it. 



The main difficulty in such photography is to keep the 

 solar image exactly tangential to the slit, but they have 

 overcome this by fitting a slipping-plate over the slit-plate. 

 This slipping-plate is moved, parallel to the slit-plate, by 

 a fine screw, and carries a right-angled prism which reflects 

 I he image of the limb on to a second, similar, prism fi.xed 

 in front of the slit so as to reflect the rays between the 

 slit jaws. The observer watches the spectrum, and by 

 moving the slipping-plate preserves the tangential position, 

 which gives the " flash " spectrum, throughout the ex- 

 posure. The lower telescope gives a solar image of 

 11-7 inches diameter, and a grating having 568 lines per 

 mm. on a ruled surface 49 mm. by 82 mm. is employed ; 

 better results are anticipated when the new 150-foot tower 

 telescope becomes available. At present provisional wave- 

 lengths are given for 124 " flash " lines, which are tabu- 

 lated to show coincidences with Rowland's solar lines and 

 with the eclipse lines observed by Evershed, Frost, Jewell, 

 and Lockyer, respectively. The deviation of the wave- 

 l>'ngths of these lines from those given by Rowland for 

 the corresponding solar lines is less than the probable error 

 of measurement; if the bright lines of the " flash " spec- 

 trum were due to anomalous refraction at the sun's edge, 

 .Ts suggested by Julius, the two sets of wave-lengths should 

 differ considerably. 



Search-ephemeris for Giacobini's Comet. 1896 V. — A 

 revised set of elements for the comet discovered by 

 Giacobini on September 4, 1896, is published by that 

 observer in No. 43C4 of the Astronomische Nachrichten, 

 and gives the probable date of perihelion passage as 

 December 19, 1909. 



Three search-ephemerides are also given, one assuming 

 that perihelion will occur on December 19-364, the others 

 for ten days before and after, respectively. The position 

 for November 4 is o=i8h. i3-im., 8 = 15° i' S., and the 

 brightness is given as 0-58, unity being about equivalent 

 to magnitude 12-0. The southerly declination and com- 

 |)nrative faintness of the object render it unlikely that the 

 comet will be observable, if found, except by the largest 

 instruments. 



NO. 208g, VOL. 82] 



THE UPPER AIR.' 

 'T'HE past decade has been very fruitful in the investiga- 

 tion of the upper air. By the use of kites sufficient 

 results have been obtained to furnish a tolerably complete 

 knowledge of the variation in the meteorological elements 

 up to a height of 2 km., while registering balloons have 

 furnished information regarding the distribution of tempera- 

 ture up to heights of 15-20 km. The results of the Berlirj 

 manned balloon ascents were arranged and discussed very 

 fully ten years ago, but no such comprehensive discussion 

 of the much more numerous kite and registering balloon 

 ascents has yet been attempted. The present report deals 

 with the instruments and methods of investigation, and 

 with the results for temperature and for wind. 



The most important series of the earlier ascents with 

 manned balloons was that made by Glaisher in 1S60-70. 

 Unfortunately, he was led to believe that artificial ventila- 

 tion of the thermometers was unnecessary, with the result 

 that his observations at great altitudes are untrustworthy. 

 In the series of ascents made from Berlin in 188S-95, 

 observations made with careful ventilation proved beyond 

 doubt that large errors would arise in the absence of proper 

 ventilation, and that Glaisher's results were almost certainly 

 affected by such errors. 



The following table shows the nature of the errors, and 

 incidentally furnishes a comparison with one of the earlier 

 ballon-sonde ascents : — ■ 



Fall of temperature " C. 



Temperature observations in manned balloons are now 

 usually taken with an Assmann's aspirator, in which a 

 ventilating current of about 4 m.p.s. is forced by a fan 

 through a polished tube containing the thermometer and 

 screening it from radiation. 



The instruments used with registering balloons are of 

 two types. In the large type the record is made on a 

 metal or photographic sheet, covered with lamp-black, and 

 wrapped round a revolving cylinder driven by a clock. 

 Pressure, temperature, and humidity are recorded by 

 separate pens. The barometer is a Bourdon tube or aii 

 aneroid, the thermometer some form of bimetallic instru- 

 ment, and the hygrometer a bundle of hairs. In the small 

 type the temperature record is traced on a cylinder or plate, 

 which is itself moved at right angles to the direction of 

 motion of the temperature lever by the changes of pressure. 

 The temperature and pressure are then given by the 

 ordinates and abscissa; of the trace obtained. The 

 advantage of this arrangement is that no clock is required, 

 and the instruinent can be made much lighter and is more 

 easily tested. The loss of the humidity trace is un- 

 important, because the hygrometric records at low tempera- 

 tuies are very untrustworthy, and the observations in the 

 lower layers can be made with kites or manned balloons. 



The instruments used with kites are similar to the 

 ballon-sonde instruments of the larger type, but they have 

 an arrangement for recording wind velocity. In the Dines 

 instrument the records are traced on a flat, circular sheet 

 of cardboard rotated by means of a clock and resting on 

 a wooden tray beneath which the instruments are placed. 



The ballon-sonde instruments are tested either (i) by 

 keeping the thermometer at ordinary atmospheric pressure 

 in testing for temperature, and the barometer at ordinary 

 temperatures in testing for pressure, or (2) by testing the 

 thermometer through the temperature range at different 

 pressures and the barometer through the pressure range at 



1 Report on the Present State of our Knowledge of the Upper Atmosphere 

 as obtained by the use of Kites, Balloons, and Pilot Balloons." Report of 

 the Committee, consisting of Messrs. E. Gold and W. A. Harwood, pre- 

 sented at the Winnipeg meeting of the British Association, 1909. 



