September 23, 1915] 



NATURE 



89 



clock rate and for '* following " in the case of 

 photographing- the spectrum of a comet. 



In order to obtain a serviceable width and the 

 necessary density to the spectra, a rate of accelera- 

 tion or retardation is given to the driving clock. 

 This rate depends on the magnitude of the star 

 in question, its type of spectrum, and its declina- 

 tion. The adjustment for rate is accomplished by 

 regulating the speed of the governor ring by 

 means of the cam mentioned above, the indicator 

 being set to readings which have been derived 

 from previous photographs. 



The McClean telescope is mounted on three con- 

 crete pillars in a building with a circular concrete- 

 block wall, internal diameter of 18 ft., on which 

 is a hemispherical dome made of wood and covered 

 with rubberoid. The wall is double — that is, has 

 an air space in order to prevent rapid changes of 

 temperature of the air in the dome. The dome 

 rests on iron wheels running on a circular rail 

 fixed to the upper part of the wall, and is easily 

 revolved by hand by means of an endless rope 

 round a grooved pulley fixed to the axis of one 

 of the wheels. The shutters, also operated by 

 hand, are made in two sections and run on rails 

 at their upper and lower extremities ; when open, 

 a clear view of the zenith is obtained. 



All the electric connections for the telescope and 

 lighting purposes and for the driving-clock wire 

 are led in a trough into an annexe in which are 

 placed the electric pendulum, small accumulators, 

 dark room, etc. 



The building is situated on the top of Salcombe 

 Hill to the east of Sidmouth ; it is 580 ft. above 

 sea-level, and commands an uninterrupted view of 

 the horizon in every direction. 



Since the instrument was first brought into use 

 in September;, 191 3, the site has been found to 

 have all the excellent observing conditions that 

 were anticipated. 



Smoke, mist, artificial-light glare are conspicuous 

 by their absence, and on only one occasion has 

 high wind in a clear sky prevented observation. 

 The hill-top is often clear when the adjacent valley 

 is filled with mist or cloud. Cloud on the top is 

 rare. 



The purity of the sky on almost all occasions 

 when free from clouds is extremely advantageous 

 ' . ir photographic observations. At South Kensing- 



n such clear, dark skies were extremely rare, 

 and then only one or two hours in the early mgrn- 

 ing were at all comparable with the conditions 

 here. The excellence of the atmospheric condi- 

 tions is well shown by the extension of the spectra 

 into the ultra-violet. A spectrogram of o Cygni 

 taken with the 9-in. Henry prismatic camera shows 

 the hydrogen series down to H^ (\ 3667*8), i.e. 

 twenty-three hydrogen lines on the one plate. The 

 most refrangible hydrogen line recorded in the 

 South Kensington reduction of the spectrum of 

 o Cygni was He {\3798). It may also be men- 

 tioned that the southern stars a Columbae (dec. 

 — 34° 8') and \ Scorpionis (dec. - 37° 2') have 

 been seen with the naked eye. The steadiness 

 of the image is normally greater than at South 

 NO. 2395, VOL. 96] 



Kensington, and long exposures on faint stars give 

 spectra showing definition of a very satisfactory 

 character. 



The working list prepared for use with the 12-in. 

 McClean instrument contains all the stars of 

 the Harvard revised photometry of magnitudes 

 fainter than 4'o and brighter than 5"o to the north 

 of dec. — 15*^ which were not included in the 

 catalogue of 470 brighter stars compiled at South 

 Kensington. For these stars exposures of twenty 

 minutes to one hour, according to magnitude and 

 type, are usually amply sufficient to yield spectro- 

 } grams of sufficient width and density to exhibit 

 enough detail for the purpose of classification. 

 Neighbouring stars fainter even than 6*0 magni- 

 tude are sometimes satisfactorily recorded. 



A catalogue of the stars the spectra of which 

 have been photographed and classified since 191 3 

 at the Hill Observatory has been prepared ; it con- 

 tains 354 stars. The designations, positions for 

 1900, magnitudes, and Harvard classification have 

 been taken from the Revised Harvard Catalogue 

 (Annals of the Astronomical Observatory of Har- 

 vard College, vol. iv.). In the last column of the 

 table is given the equivalent Kensington classi- 

 fication. The small letters h, c, and a indicate 

 whether the star is increasing its temperature 

 (hotting) (/i), decreasing its temperature (cooling) 

 (c), or at the apex (a) of the temperature curve or 

 about the condition of being most hot. The letter 

 {p) denotes that there is some peculiarity about the 

 spectrum. 



These small letters will save references to the 

 groups in my classification in the case of those 

 inquirers chiefly interested in temperatures. They 

 also show that the Harvard classification includes 

 both classes of stars under the same designation 

 in the other cases. 



Before the war Lieut. Lockyer, R.N.V.R., and 

 Mr. Johnson and Mr. Goodson were the assistants 

 engaged in photographing and classifying the 

 spectra. Since Lieut. Lockyer and Mr. Johnson 

 took up their military duties, their work has been 

 carried on by Mr. Goodson. 



Norman Lockyer. 



THE ATTACKS OF BIRDS UPON FRUIT. 



UNDER the heading of "The Ravages of 

 Birds " a correspondence has arisen in the 

 Times which is apt to mislead both the general 

 public and fruit-growers on a subject already over- 

 burdened with misrepresentation and error. 



It is suggested by one correspondent that there 

 are two simple methods for preventing the attacks 

 of birds upon fruit, viz., (i) provision of drinking 

 water, (ii) provision of food to entice the birds 

 away from the fruit. That there may be a 

 scarcity of water in some districts is quite pos- 

 sible, but at the time when the missel thrush, 

 blackbird, blackcap, bullfinch, etc., attack fruit 

 there is an abundance of animal food in the form 

 of insect larvae, insects, worms, slugs, snails, etc., 

 in addition to wild fruits and seeds. Further, if 

 a few of these fruit-eating birds are shot, and the 



