November, 1902.] 



KNOWLEDGE, 



247 



PHOTOGRAPH OF THE NEBULOUS REGION ON 

 THE FOLLOWING SIDE OF GAMMA CYGNI. 



By IsA.,vc Roberts, d.sc, k.k.s. 



The ]>hot<)<jraph annexed is of the region of the sky 

 comprised between R.A. 20h. 20m. 25s. and K A. 

 20h. 26m 50s., and in Declination between south 

 + 39' 12'0 and +40° 48'-5 north. The area, therefore, is 

 6m. 25s. ill extent ivom following to preceding and 1° 36''5 

 from north to south. Saile — one millimetre to twenty- 

 four seconds of arc. 



Co-ordinates of the fiducial stars marked with dots for 

 the epoch 1900:— 



star (.1 D.M. No. 4178. Zone +3a« R.A. -JOh. 21m. 51 'Ss. Dec. +39" 27'i). 



Mag. 7-5. 

 Sur 1.) D.M. No. 4193. Zone +39« E.A. aoh. 33iu. 7-6s. Dec. +■«)'> I'-O. 



M&^. 7 7. 

 Star (-.v D.M. No. 4188. Zone +40= E.A. 30h. Urn. 58-2s. Dec. -1-40° 34 1. 



Milt:. « 0. 



The photograph was taken with the 20-inch reflector, 

 and exposure of the plate during 90 minutes on thi' 

 5th Septemlxn-, 1901, and, like the many other nebulae 

 which I have photographed during the past fifteen years 

 (some of which have been published in Knowledge and 

 in my two volumes of Stars, Siar-Chisiers and Nehtilie), it 

 presents characteristic features of aggregation into definite 

 loci which will probably develop into separate nebulse ; 

 some of them assuming, under the stress of disturbance 

 and gravitation, the form of spiral nebulae; these again will 

 develop into stars and clusters of stars. 



In this manner does the evidence, which has Iwcu 

 accumiUated by the aid of photography and by eye 

 observations, lead us to the inference that changes — 

 eternal changes — are part of the order of Natiu-e, whether 

 we view them in the inconceivable distance of space 

 amongst the stars and nebulas, or in the smallest micro- 

 scopic compoun^^ or organism on this relatively smaU speck 

 of earth. The i-esults are consistently identical in 

 principle, that the older forms of matter are disintegrated 

 and afterwards reconstituted into new forms of aggregated 

 matter and of life. This appears to be invariably the 

 grand order of the laws of Nature. 



THE DURHAM ALMUCANTAR. 



By Prof. R. A. Saivipson, m.a. 



In the problem of mapping and measuring the skies, 

 general attention has of late years been directed mainlv 

 to the Work that ca.n be done with a photographic equa- 

 torial, that is to say, to the task of completing the 

 astrographic plates, and of devising satisfactory methods 

 of measuring and recording them. But at least among 

 those professionally engaged in astronomy tliis is not due 

 to any neglect of another and more fundamental branch 

 with which the equatorial cannot compete. One recalls 

 that Bessel gave the na.mo Futulamenta Astronomiae pro 

 anno MDCCLV. to his discussion of Bradley's transit 

 results. For the measurement of large distances upon 

 the sky and fixing all the critical points, the transit 

 circle and clock have hitherto been the sole authorities. 

 Now, no matter how good a method may be, it is always 

 preferable to check its results by a different method than 

 to repeat them. Take what precaution we mav, each 

 system almost certainly brings with it its own systematic 

 faults, which it is next to impossible to eliminate ; hence 

 there is very great importance attaching to a nadical 

 variation of t he design of instrument and system of obser- 

 vation of transit work. The transit circle has held its own 

 in the past against more than one such rival. The two 



altazimuths at Greenwich occur to us at once as instances. 

 A variation of the traditional design of transit circle was 

 suggested by the late Mr. E. J. Stone in 1881, in which 

 there was no tube at right angles to the conical axis about 

 which the instrument revolved, but in the centre of this 

 axis the light fell upon a prism which diverted the rays so 

 that the eye looked through this axis when observing, and 

 the third face of the prism was curved to give the necessary 

 deviation to the rays. This instrument was never made. 

 Up to the present time, the undivided credit of inventing 

 and using an instrument and method which are exact 

 enough to check if not to outdo the determinations of the 

 best "transit circles belongs to Mr. S. C. Chandler, of 

 Boston, U.S.A. 



" The idea occurred to me about eight years ago," Mr. 

 Chandler writes in 1887. "of substituting for the meridian 

 as a fundamental jdane of reference, the small circle 



CliaiuUer'i Almucint 



perpendicular to the meridian passing through the pole ; 

 and for the motion of rotation determined mechanically 

 by the pivots of a horizontal axis, one determined by 

 gravitative action about an imaginary vertical axis. Two 

 ways of doing this suggested themselves. The instrument 

 might be suspended like a pendulum, or it might be 

 floated upon mercury." Experiments decided in favour of 

 the latter method, and after making a small trial instrument 

 and obtaining from it results of unexpected accuracy, 

 Mr. Chandler, in the years 1884 and 1885, used facilities 

 placed at his disposal "by the director of Harvard College 

 Observatory to make a more searching study of the 

 possibilities of his invention. In this research he employed 

 a new instrument, with a telescope of 4 inches aperture. 

 It was mounted on a tripod stand, which carried a 

 horizontal trough which could rotate in azimuth ; this 



