June, 1905] 



KNOWLEDGE & SCIENTIFIC NEWS. 



131 



ASTRONOMICAL. 



By Charles P. Butler, A.R.C Sc. (Lond.), F.R.P.S. 

 Tenth Satellite of Sa-txirn. 



Another interestiiif^ communication from the Harvard 

 College Obser%-atory announces ttie discovery by Professor 

 W. H. Pickering of a new satellite to the planet Saturn, bring- 

 ing the number of its attendants up to ten. The period of 

 revolution of the new satellite is stated to be 21 days, which is 

 very nearly equal to that of the seventh satellite Hyperion. 

 The body is evidently extremely faint, as it is estimated to be 

 three magnitudes fainter than Hyperion (which is about 17), 

 so that it is doubtful if the new object will be detected visually 

 for some time. The orbital motion is believed to be direct. 



* * * 



Seasonal Changes on Mars. 



A telegraphic communication from Cambridge, U.S.A., 

 announces that Mr. Percival Lowell, at the Flagstaff Obser- 

 vatory, Arizona, has again detected the evidence of seasonal 

 changes on the Martian surface during the present opposition. 

 The observational evidence consists chiefly of colour changes 

 on the various well-known areas, and was first noticed by 

 Lampland on April 4. The most prominent feature is seen in 

 the Mare Erythrjeum, just above the Syrtis, which has again 

 altered from blue-green to chocolate-brown. The Martian 

 season at the time of observation, April g, corresponded to the 

 terrestrial February. 



* * » 



The Lens Mirror Telescope. 



In an excellently-worded booklet, Mr. G. Whittle, of Liver- 

 pool, describes the construction of a new form of lens-mirror 

 telescope that he has recently devised. In this the reflecting 

 surface consists of the back of the lens, which is silvered and 

 varnished, thus being completely protected from deterioration. 

 Moreover, the length of the telescope body is greatlv reduced. 

 The lens adopted is a concave-convex for the main mirror, 

 and a small meniscus is employed near the focus as a secondary 

 mirror on the Gregorian plan for magnification. We have not 

 had the opportunityof using the instrument, but its adaptability 

 is stated to depend mainly on its absolute achromatism, and 

 perfect intcvnal reflection from a surface of pure silver 

 deposited on a true surface of optical glass. 



The Gregorian mounting has been chosen on account of the 

 resulting image being in an erect position. 



* * * 



The New Solar Observatory on Mount 

 Wilson in California. 



Recent changes in the arrangement of the stafl'of the Yerkes 

 Observatory, resulting in the transference of its former 

 Director, Professor G. E. Hale, to the superintendence of the 

 new solar observatory established by the Carnegie Institution 

 on Mount Wilson. Pasadena. California, will probablv mark 

 an important epoch in the progress of scientific astronomical 

 investigation. 



It was only after very exhaustive preliminary tests that this 

 station was selected by Professor Hale and his colleagues, and 

 the numerous data supplied fully support their decision. 

 Situated at an elevation of nearly 6000 feet, the station affords 

 exceptional facilities for many solar investigations which 

 cannot be efliciently carried out at places nearer sea-level. 

 The plan of work outlined for the Institution includes : — 



I. Frequent measurements of the heat radiation of the sun 

 to determine whether there may be changes during the 



sun-spot cycle in the amount of heat received from the 

 sun by the earth, and in the relative radiation of the 

 various portions of the solar surface. 

 2. Studies of various solar phenomena, particularly through 

 the use of powerful spectroscopes and spectrohelio- 

 graphs. 

 3. Photographic and spectroscopic investigations of the 

 stars and nebula: with a very powerful reflecting tele- 

 scope, for the principal purpose of throwing light on the 

 problem of stellar evolution. 



From the records now in e.xistence, it appears that solar 

 observations will be possible on 300 days of the year, and the 

 mean daily range of temperature only varies from 18-5° F. in 

 April to 27- 1 = F. in November. The anemometer records indi- 

 cate that the average wind movement is exceptionally low, 

 indicating a uniform atmosphere. Operations were started 

 with a 15-inch coelostat and a lens of 6 inches aperture and 

 6ii feet focal length, and many interesting observations made 

 on"the effect of heated air rising from the ground across the 

 sit'ht line of the instrument. By raising the piers as far as 

 possible above the ground and taking special precautions for 

 eliminating variations of temperature in the observing room, 

 it has been found possible to obtain nmch better definition 

 than usual. 



.Associated with Professor Hale in the new institution are 

 Messrs. Ritchey, EUerman, and Adams, all from the Yerkes 

 Observatory. They hope to have the 5-foot Snow reflec- 

 tor available for use very shortly. Two concave mirrors 

 of 24 inches (61 cm.) aperture, 60 feet (18-3 in.) and 145 feet 

 (44-2 m.) focal length respectively are to be used for forming 

 the primary images of the solar disc. The spectroscopic 

 apparatus to be used in conjunction consists of: — 



1. A spectroheliograph with portrait lenses of S inches 

 |20'3 cm.) aperture and 60 inches ( 152 cm.) focal length, 

 provided with four dense flint prisms. This will be 

 floated in mercury, to reduce the friction on the rolling 

 surfaces. Daily photographs of the entire solar disc 

 with the calcium and hydrogen lines will be taken with 

 this, using the image of 67 inches (17 cm.) diameter 

 given by the concave mirror of 60 feet focal length. 



2. A spectroheliograph of 5 inches (127 cm.) aperture and 

 30 feet (9-I4 m.) focal length, provided with three light 

 flint prisms of 50- angles. In this instrument the spectro- 

 heliograph will remain fixed, and the traverse of the 

 image across the slit obtained by a slight rotation of the 

 large mirror, and a corresponding motion of the photo- 

 graphic plate. The whole will be used for studying 

 special zones of the solar image, and with a plane grat- 

 ing, for the study of sun spots, &c. 



3. A Littrow spectroscope of 18 feet (5-49 m.) focal 

 length, with large plane grating, to be used for study of 

 solar rotation and spectrum of sun spots. 



4. A large concave grating stellar spectrograph, of about 

 15 feet (4-57 m.) equivalent focal length, used with a 

 collimatiug lens of 5 inches (127 cm.) aperture to elimi- 

 nate astigmatism. 



5. A prism spectrograph, with collimator of i* inches 

 (3-8 cm.) aperture and 48 inches (114-5 cm.) focal 

 length ; dispersion train of one to four prisms, and 

 various camera lenses. This will be used in the deter- 

 mination of wave lengths of stellar spectra, especially in 

 the ultra violet regions. 



The activity of Professor Hale and his staff is well shown 

 by the recent publication of a beautiful reproduction from a 

 photographic spectrum of the solar surface. This shows the 

 violet region, including the H and K lines of calcium, which 

 are about 4i inches apart. This photograph was obtained at 

 Mount Wilson with the Littrow spectrograph above men- 

 tioned, the grating being 4 inches in aperture with 14.43S lines 

 to the inch, using the third order. An interesting feature of 

 the photograph'" is the strength of the reversals over the 

 regions occupied by faculas on the sun's disc, and the scale is 

 sutflcient to show clearlv that the continuous spectrum of the 

 facula: rapidly decreases in intensity as it approaches the 

 centre of Hi and Ki, where it almost disappears. This fact 

 will prove most useful in future theoretical considerations. 



