i6 



NATURE 



[May 2, 1889 



therefore forms a most necessary and valuable introduction to a 

 complete survey of the heavens on the same method. The instru- 

 ment used was the Voigtlander photographic doublet, of 8 inches 

 aperture and 44 inches focal length, so that the scale of the 

 photographs was that of the atlas of the Dmchmiisteriin^, 2 

 centimetres to a degree. The images of the stars obtained on 

 the plates were of different kinds, the clock sometimes being em- 

 ployed to drive the telescope when the stellar images were points 

 or disks, sometimes the clock was stopped when trails were 

 obtained, sometimes the clock was used but trails produced 

 through the polar axis of the telescope not being parallel 

 to that of the earth ; indeed the adjustment of the polar 

 axis was made in this way. The standard for measuring 

 the stellar points was a photograph of the Hyades, the 

 plate being exposed six times with exposures of 3 seconds, 

 and 3-, 3'', to 3" seconds respectively. For measuring trails 

 a plate was exposed to the polar region, and the aperture 

 of the telescope varied to correspond to successive differences of 

 a magnitude. The result of the careful and independent 

 measurements of the plates showed that the measures of a 

 skilled observer of the same star disk or trail did not vary on the 

 average by so much as a tenth of a magnitude ; so that if the 

 errors due to the photographs themselves can be eliminated the 

 photographic method of determining stellar magnitudes is at 

 least as efficient as the best photometric methods. The com- 

 parison of the diurnal with the clock trails showed that the cor- 

 rection for declination to be applied to the former was only half 

 2 "5 log cos 5, the value it should have had if the chemical action 

 due to a certain amount of energy was independent of the time 

 during which it acted. 



The first of the three catalogues given in this work is that of 

 the stars within 1° of the pole. Rectangular co-ordinates are 

 given with the stars, instead of R.A. and declination. Of the 

 IC09 stars included, 947 are within one degree radius from the 

 pole, and nearly all are above the fifteenth magnitude. The cata- 

 logue of the Pleiades includes all of Wolf's stars between 3m. 

 preceding, and 2m. following .Alcyone, and 30'north and 15' south 

 of that star with a few apparently overlooked by Wolf. The 

 equatorial catalogue contains the stars within 2° of the equator. 

 Ten different fields were photographed on each plate, one 

 being exposed on the meridian, eight others right and left at in- 

 tervals of 40m. hour angle, and the tenth on the polar region. 

 A comparison of the results obtained brings out some interesting 

 points. Tempel, at Marseilles, observing the Pleiades with a 

 4-inch telescope, reached fainter stars than Wolf at Paris with 

 12 inches aperture. The behaviour of photographic lenses 

 of different apertures shows that to double the aperture is to 

 command two additional magnitudes ; to treble it, two and a 

 half. A 24-inch aperture should, therefore, grasp stars below 

 the seventeenth magnitude. A comparison t»f the photographic 

 magnitudes with the Cordoba Catalogue, and the Durchmusterung 

 gives distinct maxima for the residuals in the Milky Way, 

 showing that the Catalogue magnitudes are too faint near the 

 Galactic stream where stars are numerous. 



ASTRONOMICAL PHENOMENA FOR THE 



WEEK 1889 MA F 5-1 1. 



/"POR the reckoning of time the civil day, commencing at 



^ Greenwich mean midnight, counting the hours on to 24, 



is here employed.) 



At Greenwich on May 5 

 Sun rises. 4h. 26m. ; souths, iih. 56m. 32*03.; daily decrease 

 of southing, S'ls. ; sets, igh 27m. : right asc. on meridian, 

 2h. 507ni. ; decl, i6° 23' N. Sidereal Time at Sunset, 

 loh. 22m. 

 Moon (at First Quarter on May 8, 

 souths. i6h. 17m. ; sets, oh 35m.*: 

 7h. 117m. ; decl. 22° 41' N. 



7h.) rises, 7h. 57m. ; 

 right asc. on meridian, 



May. 

 5 • 



h. 

 17 



Mercury in conjunction with and 1° 9' north 

 of Mars. 



7 ... 22 ... Saturn in conjunction with and 1° 28' south 

 of the Moon. 



Saturn, May 5. — Outer major axis of outer ring = 4i"'0: 

 outer minor axis of outer ring = ii"*6 : southern surface visible. 



GEOGRAPHICAL NOTES. 



The discovery is announced of a new mouth of the Zambesi, 

 forty-five miles south of the Quaqua, on which Quillimane is situ- 

 ated. The name of the river is Chinde. As we know already of a 

 Chinde River which joins two of the principal mouths of the 

 Zambesi, the probability is, not that a new mouth has been dis- 

 covered, but that an already known mouth has been more 

 completely explored. The Chinde, it seems, has a channel 

 some 500 yards wide, with three fathoms of water at the lowest, 

 and is therefore expected to afford a clear waterway to the main 

 Zambesi. 



For the last few years Baron Nordenskiold has been engaged 

 on a work of great importance in the history of geography, and 

 especially of cartography. He has been collecting from the 

 archives of various European countries speci i.ens of the earliest 

 printed (as distinguished from manu>cript) map^, and some of his 

 finds are really original discoveries. These he intends to repro- 

 duce in a great atlas with accompanying text, in which, among 

 other things, he will describe and discuss the various editions of 

 Ptolemy ; of these he has formed a unique collection. The 

 work will appear both in a Swedish and an English edition. 



The country of Oklahoma, about which we have heard so 

 much during the past fortnight, is in the very heart of what is 

 known as the Indian Territory, which lies between Kansas on 

 the north and Texas on the south. Although on the Survey 

 maps of the United States it seems to be well watered, the 

 actual results would show that the water is not well distributed. 

 It is traversed by the Canadian and Cimarron rivers, and between 

 them are found on the map a perfect network of streams. The 

 area of Oklahoma is a little over 3000 square miles, equal to 

 about one-twentieth of the total area of the Indian Territory ; 

 the number of Indians in the latter is about 80,000. 



In an article in the May number of the Fortni-yhtly Review, 

 by Mr. F. C. Selous, the well-known South African hunter and 

 explorer, we find a useful account of Mashonaland, around which 

 at present there is so much interest. No man knows the 

 country so well as Mr. Selous, who during the past ten years has 

 traversed it in all directions. Mashonaland lies to the north-east 

 of the Matabele country, and is described as a land of perennial 

 streams, where thirst is an unknown quantity. The high plateau, 

 which is of very great extent, forms the watershed between the 

 Zambesi to the north and east, and the Limpopo and the babi 



