January, 1907.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



The instrumental equipment includes a twin equa- 

 torial of 6i-inch aperture, the visual of 8 feet focus and 

 the photog-raphic of 7 feet, with an enlarger giving- an 

 8-inch image, an Evershed 2-slit spectroheliograph, a 

 spectrogoniometer, and a prominence spectroscope. 

 These, with a Grubb coelostat and a Rowland grating 

 practically complete one department. 



Most of the meteorological registers are obtained 

 with Richard instruments, but there are other forms of 

 apparatus — for measuring the total number of ions per 

 volume of atmosphere (Gerdien), the relative num- 

 bers of positive and negative ions (Elster and Geitel), 

 Hertzian waves (Branly), and electrical potential (Mas- 

 cart). An Arago actinometer with black and bright 

 bulbs in vacuo is employed, and an Angstrom pyrohelio- 

 meter, as recommended by the Solar Union, whose 

 Oxford meeting Father Cirera attended. In addition 

 to the Besson nephoscope is another with a wide angle 

 lens in the roof of a sort of kiosk, which produces an 

 image of the sky and clouds on a table below, some- 

 thing after the manner of a camera obscura, rendering 

 measurement very simple. 



One interesting feature of the photographic magneto- 

 graphs is the use, instead of " hour " breaks, of an 

 extra lamp onlv lighted at the hours, causing a black 

 line across the trace instead of a white one, and en- 

 abling the adjustment of the "hour" light for any 

 period from i to 80 seconds as required. 



Time presses, and we must leave many interesting 

 details, only noting that a daylight time signal being 

 insufficiently conspicuous, owing ,to distance from the 

 centres of activity, where it would be of value, a night 

 signal with white and green lights has been substi- 

 tuted, ending at g p.m. The neighbouring Jesuit 

 college for advanced students, to which, in a sense, the 

 observatory is an annexe, provides some assistance, 

 and demands some training and lectures, and there are 

 also regular days and hours for visitors. 



For the eclipse, preparations on a special scale were 

 made. - Jesuits from all parts of the world were freely 

 invited to Spain, and though many well-known 

 scientists declined, owing to press of other work, yet 

 quite a large number accepted, and arrangements were 

 made to spread out along the .Spanish totality track 

 such of the visitors as brought their own equipment, 

 leaving those totally unequipped to assist either at the 

 new observatory or elsewhere, in order not to risk loss 

 through too great concentration. 



Briefly, the local programme comprised visual ob- 

 servations of times of contact and chords, photographic 

 observations of internal contacts, spectroscopy, polarisa- 

 tion, photography and drawings of the Corona, photo- 

 metric observations, shadow-bands, atmospheric ionisa- 

 tion and electric potential, Hertzian waves, and solar 

 radiation; also atmospheric temperature and humidity, 

 observations of plants and animals, variation of 

 magnetic elements, and earth currents. 



It was unfortunate that light clouds in great measure 

 interfered with the more delicate spectroscopic part of 

 the programme, and to a less extent with other por- 

 tions, but the truly comprehensive nature of the pro- 

 gramme gives a good indication of the scope and possi- 

 bilities of the new observatory, while in some direc- 

 tions, notably in the magnetic observations, so strongly 

 insisted on by the editor of Terrestrial Magne/ism, a 

 distinct success appears to have been achieved. The 

 smaller expeditions to other places in the zone, in- 

 cluding that under Father Cortie at \'inaroz, and of the 

 German Jesuits at Burgos, were more or less successful, 

 but do not .so conspicuously belong to our present 

 subject. Illustrations from " Memoires de L'Observa- 

 toire de L'Ebro." No. i. 



Lord R.osse's Smsiller Telescope. 



By THE Rev. J. T. W. Claridge, M.A., F.R.A.S. 



The knowledge of the existence of the far-famed Lord 

 Rosse's 6 ft. Reflector and its achievements comes to the 

 vast majority of the public from magazine sketches and 

 photographs ; but few, comparatively speaking, are 

 aware even of the existence, or of the important and 

 delicate work accomplished by the 3 ft. Reflector, as seen 

 in the photograph which we here exhibit. These won- 

 derful instruments may be mentally pictured and con- 

 jectures entertained as to their actual appearance and 

 situation, but those who have never seen these great and 

 powerful searchers of the heavens can form no idea of 

 the quietude and loveliness of their surroundings. On 

 one side is a large lake bordered with trees and covered 

 with water-lilies, its still surface only disturbed by 

 numerous wild-duck and other water-fowl. On the other 

 is the majestic castle with its lawns and terraces, merely 

 a stone's throw from the world-renowned telescopes. 

 The builder of these, \Mlliam Parsons, third Earl of 

 Rosse, and father of the present Earl, was born at York, 

 June 17th, 1800. He succeeded to the title and estates in 

 1S41. It was as far back as 1827 that his scientific mind 

 encouraged him to experiment on the improvement of the 

 reflecting telescope (for he had no experience whatever in 

 the construction of the refractor), and to this object the 

 whole of his attention was directed. 



Sir \Vm. Herschel was the first to construct a reflector 

 on a large scale, but he was not altogether so very 

 successful, though he made specula — one of 18 m. 

 diameter, and one of 4 fest — for his 40 feet telescope. Un- 

 fortunately he never left any written account of his 

 methods. Consequently Lord Rosse had very little as- 

 sistance to guide him onwards to the goal of success which 

 he ultimately reached. To grind a speculum of only 6 

 or 8 inches in diameter in those bygone days was a work 

 of no ordinary labour and skill, and such a one was then 

 considered of great size. A gentleman of the name of 

 Ramage possessed a reflector of 15 in. diameter, and a 

 focal length of 25 feet, and this was for a long time the 

 largest actually in use, for, although Sir \\'. Herschel's 

 was much larger, it appears that he very seldom used it. 

 Notwithstanding the difficulties that confronted him, 

 added to the apparently sinall successes of his pre- 

 decessors, the indefatigable nobleman, endowed as he was 

 with such remarkable mechanical and mathematical skill, 

 untiring patience, and a dogged perseverance, set about his 

 arduous work with a zeal that by-and-by crowned all 

 his efforts with triumph. After many trials as to what 

 combination of metals was the most advantageous for 

 specula, as regards their whiteness, porosity, and hard- 

 ness, he discovered that copper and tin when united in 

 their atomic proportions — viz., copper I26-4 parts to tin 

 58-9 parts — was the best. This compound is of a brilliant 

 lustre and hardness, yet very brittle, and with a specific 

 gravity of 8 8 was found to be freer from pores than any 

 other with which he was acquainted. Having thus 

 ascertained the desired proportions, he set about casting 

 the speculum. The difficulties attending this process 

 were such that, instead of having the reflector, which was 

 to be 3 feet in diameter, in one piece (which was sub- 

 sequently done), he tried the expedient of casting it in 16 

 separate portions. When cast, these pieces were fixed on 

 a bed of zinc and copper, mixed in the proportion of 2-75 

 of the latter to i of the former, a species of brass which 

 readily expanded in the same degree as the speculum 

 metal. The several pieces were then ground as one body 

 to a true surface, and when soldered and polished were 



