October 22, 1891] 



NA TURE 



605 



general principles to start with. No person who is not 

 grounded in such broad principles can properly appreciate 

 the explanation of the phenomena with which his daily ex- 

 perience brings him into contact, and if his previous training is 

 insufficient lo enable him to understand ihe nature of the 

 changes which occur in the course of his operations, he cannot 

 derive any advantage from technical instruction. These remarks 

 will, I hope, serve to emphasize a distinction which exists 

 between technical chemistry and other technical subjects, and I 

 have thought it desirable to avail myself of the present oppor- 

 tunity of calling particular attention lo this point, because it is 

 one which is generally ignored in all discussions on technical 

 education. 



"The reason for this difference in the mode of treatment of 

 chemical subjects is not difficult to find. The chemical tech- 

 nologist — the man who is engaged in the manufacture of useful 

 products out of certain raw materials — is, so far as the purely 

 scientific principles are concerned, already at a very advanced 

 stage, although he may not realize this to be the case. The 

 chemistry of manufacturing operations, even when these are of 

 an apparently simple kind, is of a very high order of complexity. 

 There are many branches of chemical industry in which the 

 nature of the chemical changes undergone by the materials is 

 very imperfectly undeistood ; there is no branch of chemical 

 industry of which the pure science can be said to be thoroughly 

 known. For these reasons I believe that I am justified in 

 stating that the chemical technologist is working at a high level, 

 so far as the science of his subject is concerned, and this 

 explains why he cannot be dealt with by the analytical method. 



"The general considerations which have been offered apply 

 to the special subject of photography with full force. A per.^on 

 may become an adept as an operator without knowing anything 

 of physics or chemistry ; there are thousands of photographers 

 all over the country who can manipulate a camera and develop 

 and print pictures with admirable dexterity, who are in this 

 position. If we adopt the narrow definition of technical instruc- 

 tion, v\e should appoint such experts in our Colleges, and 

 through them impart the art of taking pictures to thousands of 

 others. But would our position as a photographing nation be 

 improved by this process? I venture to think not. We might 

 be carrying out the ideas of certain technical educators by 

 adopting this method, but I do not imagine that in the long run 

 the subject itself would be much advanced ; our position in the 

 scale of industry would not be materially raised by the wholesale 

 manufacture of skilful operators. And so with all other branches 

 of applied chemistry ; it is technologists whose knowledge is 

 based on a broad foundation that are wanted for the improve- 

 ment of our industries. These are the men who are raised in 

 the technical high schojls of the Continent, and whose training 

 the Continental industries have had the wisdom to avail them- 

 selves of." 



AN ASTRONOMER'S WORK IN A MODERN 

 OBSERVATORY.^ 



T^IIE work of astronomical observatories has been divided 

 into two classes, viz. astrometry and astrophysics. The 

 fiist of these relates to astronomy of precision, that is to the 

 determination of the positions of celestial objects ; the second 

 relates to the study of their physical features and chemical 

 constitution. 



Some years ago the aims and objects of these two classes of 

 observatories might have been considered perfectly distinct, and, 

 in fact, were so considered. But I hope to show that in more 

 recent years their objects and their processes have become so 

 interlaced that they cannot with advantage be divided, and a 

 fully equipped modern observatory must be understood to 

 include the work both ol astromclry and astrophysics. 



In any such observatory the principal and the fundamental 

 instrument is the transit circle. It is upon the position in the 

 heavens of celestial objects, as determined with this instrument 

 or with kindred instruments, that the whole fair superstructure 

 of exact astronomy rests ; that is to say, all that we find of 

 information and prediction in our nautical almanacs, all that 

 we know of the past and can predict of the future motions of 

 the celestial bodies. 



' Friday Evening Discourse delivered at the Royal Institution by Dr. 

 David Gill, F. R.S., Her Majesty's Astronomer at the Cape of Good Hope, 

 on May 29, 1891. 



He>e is a very .«n:all ard imperfect irodeJ, tut it will serve 

 to render intelligible the photograph of the actual instrument 

 which will be subsequently projected on the screen. [Here the 

 lecturer described the adjustments and mode of using a transit 

 circle.] 



We are now in a position to understand \ holographs of the 

 instiument itself. But first of all as to the house in which it 

 dwells. Here, now on the screen, is the outside of the maia 

 building of the Royal Observatory, Cape of Good Hope. I 

 select it simply because, being the observatory which it is my 

 privilege to direct, it is the one of which I can most easily 

 procure a series of photographs. It was built during the yeara 

 1824-28, and like all the observatories built about that time, 

 and like too many built since, it is a very fair type of most of 

 the things which an observatory should not be. It is, as you 

 see, an admirably solid and substantial structure, innocent of 

 any architectural chaim, and so far as it affords an excellent 

 dwelling-place, good library accommodation, and good rooms for 

 computers, no fault can be found with it. But these very 

 qualities render it undesirable as an observatory. An essential" 

 matter for a perfect observatory should be the posssibiliiy to 

 equalize the internal and the external temperature. The site 

 of an instrument should also be free from the immediate 

 surroundings of chimneys or other origin of ascending currents 

 of heated air. Bolh these conditions are incompatible with 

 thick walls of masonry and the chimneys of attached dwelling 

 houses, and therefore, as far as possible, I have removed the 

 instruments to small detached houses of their own. But the 

 transit circle still remains in the main building, for, as will be 

 evident to you, it is no easy matter to transport such an 

 instrument. 



The two first photographs show the instrument, in one case 



pointed nearly horizontally to the north, the other pointed 



rearly vertical. Neither can show all parts of the instrument, 



but you can see the massive stone piers, weighing many tons 



each, which, resting on the solid blocks 10 feet below, support 



the pivots. Here are the counter-weights which remove a great 



part of the weight of the instrun ent from the pivots, leaving 



only a residual pressure sufficient to enable the pivots to preserve 



the motion of the instrument in its pioper plane. Here are the 



microscopes by which the circle is read. Here the opening 



I through which the instrument views the meridian sky. The 



j obierver's chair is shown in this diagram. His work appears 



I to be very simple, and so it is, but it requires special natural 



i gifts, patience and devotion, and a high sense of the importance 



of his work to make a first-rate meridian observer. Nothing 



appaiently more monotonous can be well imagined if a man is 



" not to the manner born." 



Having directed his instrument by means of the setting circle 



to the required altitude, he clamps it there and waits for the 



! star which he is about to observe to enter the field. This is 



[ what he sees. [Artificial transit of a star by lantern.] 



I As the star enters the field it passes wire after wire, and as 



it passes each wire he presses the key of his chronograph and 



records the instant automatically. As the star passes the 



middle wire he bisects it with the horizontal web, and again 



similarly records on his chronograph the transit of the star over 



the remaining webs. Then he reads off the microscopes by 



which the circle is read, and also the barometer and thermometer, 



in order afterwards to be able to calculate accurately the effect 



of atmospheric refraction on the observed altitude of the star ;. 



and then his observation is finished. Thus the work of the 



meridian observer goes on, star after star, hour after hour, and 



! night after night ; and, as you see, it differs very widely from 



the popular notion of an astronomer's occupation. It presents 



no dreamy contemplation, no watching for new stars, no 



unexpected or startling phenomena. On the contrary, there is 



beside him the carefully prepared observing- list for the night, 



I the previously calculated circle setting for each star, allowing 



] just sufficient time for the new setting for the real star after the 



readings of the circle for the previous observation. 



After four or five hours of this work, the observers have had 

 enough of it ; they have, perhaps, observed fifty or sixty stars, 

 they determine certain instrumental errors, and betake them- 

 selves to bed, tired, but (if they are of the right stuff) happy 

 and contented men. At the Cape we employ two observers— 

 ' one to read the circle, and one to record the transit. Four 

 obseivers are emph yed, and they are thus on duly each alter- 

 nate night. Such is the work that an outsider would see were- 

 he to enter a woiking meridian observatory at night, but he- 



NO. II 47, VOL. 44] 



