Septemukk, l')n. 



KNOWLEDGE. 



371 



progress at Albany with a large force of computers, 

 so that astronomers will not have to wait many 

 N'ears, as is usual with most meridian work, before 

 the catalogue is published : Professor Boss believes 

 in expeditious work. 



In the summer of the present year it is anticiiiated 

 that the Olcott meridian circle will be again installed 

 and ready for work at the Dudley Observatory. 

 .\lban\-. The standard stars will be again observed 

 as already described, and, later on. the observation 

 of all the stars down to the seventh magnitude that 

 are north of —20" will be undertaken. 



I will conclude these "Notes," by a quotation from 

 a letter from Professor Boss to me: — "The last obser- 

 vation \\as taken (at San Luis) on Jan. 30, 191L 

 This work has been accomplished at a rate far beyond 

 m\- anticipations. The great prevalence of clear 

 nights — two hundred and eighty per aiiniiin — the 

 large force of observers — seven to ten, and the resist- 

 less zeal of the staff are responsible for this." As an 

 old meridian-circle observer it is pleasant to read this 

 appreciation of the observer's work, which, somehow, 

 has usuallv escaped inclusion in the introductions to 

 observatory star catalogues. 



THE A.STROXOMY SFXTION AT THE CORONATION EXHIBITION. 



The admirable principle of dexoting a section of a large 

 exhibition to Science, which was first instituted at the Franco- 

 British Exhibition at the White City, in 1908, and repeated at 

 the Japan-British Exhibition last year, has received increased 

 development at the Coronation Exhibition this year. Much 

 might be said of the exhibits in the several branches of Science 

 there shown, but our present remarks must be confined to 

 those in the section devoted to .Astronomy. 



These exhibits are deserving of more than a passing notice, 

 as they embrace some of the most recent results in astro- 

 nomical research. They consist generally of a collection of old 

 astronomical instruments, models, and photographs of celestial 

 phenomena. 



Many of the instruments have been exhibited at previous 

 exhibitions — notably the very fine and varied collection of 

 Astrolabes, Quadrants, Nocturnals and Dials shown by Mr. 

 Lewis Evans. Seeing that such were the only instruments 

 possessed by astronomers for many centuries for determining 

 the positions of the heavenly bodies and for giving the time, it 

 is interesting to examine the differences in construction and 

 estimate the very limited accuracy that was possible with such 

 instruments. Mr. Evans shows Oriental and European 

 Astrolabes dating from the fourteenth to the seventeenth 

 centuries, and a large collection of Sun Dials and Quadrants 

 of the sixteenth and seventeenth centuries. In this connection 

 there is a very interesting exhibit from Gonville and Cains 

 College, Cambridge, of an astrolabe presented to the College 

 by John Cains, one of its founders — the case of which is richly 

 embossed and of peculiar beauty. Four examples are exhibited 

 of the Davis Quadrant or Back Staff, one of which is shown 

 by Mr. Lewis of the Royal Observatory, Greenwich, who has 

 contributed a very interesting account, with a drawing, of the 

 method of using it. From this we learn that the Back Staft' 

 was invented by Captain John Davis, in the year 1590, previous 

 to his sailing for the South Seas. Before that time the only 

 means of measuring the altitude of the sun was with a simple 

 quadrant, such as the very fine specimen by Magini, shown at 

 the Exhibition. The arc of the Davis quadrant was divided 

 into degrees, and had in addition a Gunter's scale for sub- 

 divisions. A Vernier was not applied till about 1518. Some 

 fifteen years later Elton, the clockmaker, added an index arm 

 on which he placed a level which made the observer indepen- 

 dent of the horizon. A further improvement was made sixty 

 years later by Flamsteed. who added a lens to the instrument, 

 and thus it was used until Hadley invented his (juadrant in 1 730. 



Perhaps the most interesting exhibits in the Astronomy 

 Section are those contributed by the Royal Observatory, 

 Greenwich, which embrace two models of remarkable interest. 

 The first is a model of the orbit of Jupiter's Eighth Satellite, 

 showing the path of the satellite round Jupiter from the time 

 of its discovery in 1908 to the year 1916, predicted from 

 observations made in 1908 and 1909, by a method devised by 

 Dr. Cowell, the necessary calculations being made by Dr. 

 Crominelin. It is doubtful whether an astronomical model so 

 instructive as this has ever been constructed. The path of the 

 satellite is indicated by wires supported by pillars at every 



three hours of Joxicentric Right ."Ascension. The path of the 

 satellite from 1909 to 1910 is shown by a different coloured 

 wire for each year. It will be remembered that the motion of the 

 satellite is retrograde — the mean sidereal period of revolution 

 is nearly two years — the mean distance is fourteen millions of 

 miles and the mean eccentricity 0-38. The result of this 

 great eccentricity is that the distance of the satellite from 

 Jupiter varies from eiglit to twenty-one million miles, and the 

 Greenwich description of the model states that it is possible 

 for the eighth satellite to be nearer to its primary than the 

 seventh. The model gives also the orbits of satellites thus VI. 

 and VII. and the five inner satellites to scale in their proper 

 phase. The scale of the model is eighty inches = one solar 

 unit, or one inch = one million and one hundred and sixty 

 thousand miles. 



The second model referred to is that of a star cluster in 

 Taurus which has been shown by Professor Boss to form a 

 connected group of stars moving through space in the same 

 direction and with a common velocity. The exceptional 

 interest that attaches to this model warrants us in appending 

 the description of it given by the Royal Observatory. 

 " This model represents a cluster of bright stars which is com- 

 paratively near the earth. The group covers an area in the 

 sky fifteen by fifteen degrees, and is situated in the region of 

 the Constellation Taurus. From a study of their Proper 

 Motions, Professor Boss has shown that they form a connected 

 cluster of stars, moving with a common \elocity and in 

 par.allel directions. The present position of the Sun, with 

 regard to the cluster, is shown by the large white ball placed 

 at the end of the arm projecting in front of the model, the 

 plane of the base board being that of the Earth's Equator. 

 The wire along which the white ball runs represents the path 

 traversed by the Sun (or the parallel to that traversed by the 

 cluster ; for we may consider the Sun to be mo\ing past the 

 cluster, or the cluster past the Sun). The small column to the 

 left of the model indicates the position of the Sun eight 

 hundred thousand years ago. At the present time the dis- 

 tance of the Sun from the centre of the cluster is eight 

 hundred billion miles, or (say) eight million times the 

 distance of the Earth from the Sun. Relatively to the 

 Sun the cluster is moving at a velocity of twenty-eight and a 

 half miles per second, a velocity which will carry a star eight and 

 a-half times the distance of the Earth from the Sun in a year. 

 The distances of the stars in the cluster from their nearest 

 neighbours are much the same as the distance of the Sun from 

 its nearest neighbours, and all the stars in the cluster would 

 be included in a sphere of one hundred and thirty billion 

 miles radius. At present the stars are of magnitudes from 

 three and a half to six and a half; after sixty-five million years 

 the group will appear as a globular cluster about twenty 

 minutes of arc in diameter, consisting of stars from ninth to 

 twelfth magnitude. Of these forty-one stars, fourteen are 

 white stars, whose spectra are like that of Sirius : the spectrum 

 of the others show them to be in a somewhat more ad\anced 

 stage, but only a few of them have reached the stage at which 

 the Sun now is. They appear to be stars of great 



