56 



NA TURE 



{Nov. 19, 1885 



position of the wires and make-circuit lever, and tables 

 of the results, and says, finally : — 



" The simplicity and inexpensiveness of the chrono- 

 scope we have described in this paper, its accuracy, and 

 the ease with which it is used, must commend it to all who 

 will give it a trial under the conditions of the action 

 which we have endeavoured to set forth in this paper. 

 Another of its advantages is that its records on the paper 

 covering the cylinder are easily rendered permanent by 

 drawing the unsmoked side of the paper over the surface 

 of a dilute solution of photographic negati\e varnish con- 

 tained in a wide sliallow dish. On the records may be 

 written with a blunt style the nature of the experiments 

 they record before the carbon is fixed by the varnish, 

 and then they can be bound together in book-form for 

 preservation and reference." 



Alexander J. Ellis 



HINTS ON THE CONSTRUCTION AND 

 EOUIPMENT OF OBSERVATORIES FOR 

 AMATEURS 



IF it were necessary to offer any apology for the short 

 series of articles of which the first is now presented 

 to the readers of Nature, it might be found in the fact 

 that, so far as I know, nothing fulfilling the above title 

 has been put into circulation in England for more than 

 forty years. This is the more remarkable when one con- 

 siders the great development of astronomy in this country 

 during the present generation, a development the credit 

 of which is far more due to amateur effort than to the 

 influence of Governments or public establishments. The 

 reason I have fixed upon the year 1844 is that that was 

 the year in which Admiral .Smyth published his well- 

 known " Bedford Catalogue of Celestial Objects," to which 

 he prefixed certain chapters dealing with the construction 

 and management of small observatories. 



Those chapters have never been reproduced in any 

 form, partly, no doubt, for the reason that they are a good 

 deal out of date ; but they are still capable of furnishing 

 many useful hints to any one who wishes to write on the 

 subject of observatories. 



It is not too much to say that the Bedford Observatory 

 has directly or indirectly served as the model for nearly 

 all the private observatories of moderate dimensions since 

 erected in England, and it is equally certain that, what- 

 ever may be the changes which considerations of finance, 

 or architecture, or geology, may render expedient in par- 

 ticular instances, no important alterations need be made 

 in the main features of the Bedford Observatory, although 

 upwards of half a century has elapsed since it was erected, 

 and more than forty years have passed away since it was 

 pulled down. 



In order to compress as much information as possible 

 into a small compass I propose to classify what I have to 

 say in such a way as shall successively conduct the reader 

 step by step through the stages which he himself will have 

 to pass through between the time when he determines to 

 erect an observatory and the time when he finds himself 

 the happy possessor of the completed building. Of tele- 

 scopes as such I shall here say nothing, and the only other 

 prefatory remark which seems requisite is this : that an 

 amateur astronomer with only a given and moderate sum 

 of money to lay out will do well to appropriate an ade- 

 quate part of his funds to the purchase of a fairly good 

 stand and of a suitable structure in which to house his 

 instruments, rather than spend too much on his tube and 

 then be obliged to starve the stand and to put up with 

 inadequate shelter from the weather or no shelter at all. 

 To begin, therefore, at the beginning. 



The Choice of a Site. — As to this the amateur will 

 probably in most cases be obliged to suit himself as best 

 he can. If his garden otters any varieties of site, he 

 should endeavour to secure one on slightly rising ground. 



with an uninterrupted horizon to the south (for meridian 

 purposes) and to the west (for comets and inferior planets 

 in the vicinity of the sun at sunset). A clear horizon to 

 the east is of less inoment, unless searches for comets 

 before sunrise are intended to be systematically carried 

 out. 



In making preparations for building an astronomical 

 observatory — and occasionally, indeed, for other purposes 

 —it is necessary to know how to set out a meridian line. 

 Of course this may be done by means of a mariner's 

 compass (correcting for the magnetic deviation) ; but 

 there are other ways of doing this independently of a com- 

 pass, and as it is not always easy to ascertain the devia- 

 tion a statement of at any rate one of these other ways, 

 as given by Challis, will be useful. .Set up a pole at the 

 spot through which the proposed meridian line is required 

 to pass, using a plumb-line to ensure the pole being 

 vertical. Draw around the pole as a centre several con- 

 centric horizontal circles, and mark the points of coin- 

 cidence of the extremity of the shadow of the pole with 

 these circles both before and after noon. Then if the 

 two points on each circle be joined by a chord the mean 

 of the directions of the middle points of the chords from 

 the pole will be approximately the direction of the 

 meridian line. This method answers best about mid- 

 summer when the sun's diurnal path is high in the 

 heavens, and the change of declination is small. A little 

 forethought must be displayed in suiting the dimensions 

 of the circles to the height of the vertical pole employed. 



pl.in of the Bedford Observatory. 



Foundations. — The foundations of an observatory 

 are a matter of great importance, and unless a rock ' or 

 chalk bottom can be readily obtained, an artificial 

 bottom of concrete, more or less thick according to the 

 height of the intended superstructure, must be made. 

 This of course applies to the piers which are to carry 

 instruments. In the case of the observatory itself, 

 especially if the material of the fabric is to be of wood, 

 which is so often used, the ordinary precautions against 

 settlement taken by a competent builder will suffice. As 

 no fire-place is permissible in an observatory because of 

 the disturbing currents of air to which fires give rise, 

 special precautions must be taken to protect the build- 

 ing and its contents against aamp, and the consequences 

 thereof. In heavy clay soils clear away the soil all around 

 the outside of the observatory by making a trench, say 

 10 feet wide and 4 feet deep, and fill up the excavation 

 with broken bricks, coarse gravel, or other hard porous 

 material. Provide by suitable gutters and pipes, that all 

 rain-water falling on the observatoiy shall be carried 

 away to a distance as quickly as possible. 



Details of the Structure of the Observatory. — Fig. i 

 represents the ground plan and Fig. 2 the elevation of 

 the Bedford Observatory. The external dimensions were 

 about 35 feet by 13 feet 6 inches. The building was 

 divided into two apartments: (i) an equatorial room, 

 circular, and 15 feet in diameter on the inside; and (2) 

 a transit-room, 17 feet by 12 feet on the inside, and 10 feet 



ist stable possible, and some 



rily the 

 ndy substratum best. 



