NATURE 



[November ii, 1897 



The Binary & 395 = 82 CETi.-Dr. T. J. J. See has found 

 a most interesting double system in the binary & 395, which 

 Barnham was the first to detect (1875) and the last to measure 

 (1891-8). The object was detected with Dr. See's usual sweep- 

 ing power, namely 500, but before the components could be 

 well divided he had to employ a power of 1500. At first the 

 s)stem was supposed to be new, owing to the great difficulty of 

 observing it, but a search showed that it was none other than 

 the system mentioned above, its cordinates being 



o = oh. 32m. 9-9$. 5 = -25° 18' 37"-3 (1900-0). 

 The most striking feature of this binary is that since its last 

 measurement the orbital motion has been so great that the 

 whole aspect of the system is changed. Nearly one and a 

 half revolutions have been performed since 1875, and, curiously 

 enough, as the companion relumed to the same general position 

 in 1886, the " observers of that and the following years failed 

 to recognise that any sensible motion had intervened." 



Dr. See has calculated from all the published observations 

 the orbit of this binary {Astr. Nachr., No. 3455), and he finds 

 it of great eccentricity and revolving in the short period of 

 16-3 years. 



Thus 82 Ceti becomes an important sy.stem, and should be 

 carefully watched during the next eight years. Only three other 

 systems revolve more rapidly, namely, ^ 883 in 5-5 years, 

 K Pegasi in 1 1 -42, and 8 Equulei in 1 1 45 years. 



Telkscopic Seeing.— The Lowell Observatory is not of a 

 fixed but of a migratory nature. Like a bird which at some 

 period of the year changes its locality for warmer climes, so this 

 obseryatf.ry is moved to a region where the air is more suited at 

 that time for better telescopic seeing. Oscillating between Flag- 

 staff, Arizona, and Tacubaya, Mexico, Mr. Lowell is able to 

 take advantage of the periods of good seeing at each of these 

 stations. Both localities satisfy the now well-known geo- 

 graphical and meteorological conditions, and while Flagstaff is 

 rather too far north, bordering on the great cyclonic movement 

 in the north temperate zone in winter, the neighbourhood of the 

 city of Mexico is not affected by this disturbance. The latter 

 station is not, however, found to be ideal, owing to conditions of 

 local topography. What these conditions are will be found 

 stated by Mr. Lowell in his discussion on the capabilities of 

 these two stations {The Observatory iox^ov^mh^x. No. 259). 



The well-known observer, Dawes, always used to judge the 

 " goodness" of the night by the size of aperture that could be 

 satisfactorily used ; thus he would speak of a one-inch night, 

 three-inch night, up to an eight-inch night, his largest aperture 

 being of eight inches. We are now finding out how accurate this 

 system was, for, owing chiefly to the work of Mr. Douglass, the 

 controversy between large and small apertures seems to be a 

 question of the wave-lengths of the air-waves. An idea of the 

 nature of these small air-waves will be gathered from Dr. See's 

 interesting article in \hQ Astronomische Nachrichten {^o. 3455), 

 and the diagrams shown illustrate the main conditions for good 

 and bad seeing. These waves vary in different currents from 

 half an inch to several feet. In cases where they move in the 

 same direction and at a great rate the seeing is very bad. With 

 moderate-sized waves moving slowly the definition is generally 

 very fair. Often cross-currents occur, and when fine waves 

 move in all directions the definition is never good, but for 

 cases of very fine seeing only very slight traces of gently 

 moving waves can be discerned. Theoretically for the best see- 

 ing there should be no trace of movement at all. Dr. See points 

 out, in another article in the same journal, that the scintillation 

 of the fixed stars can be very easily explained on this wave 

 theory, and the experiments which he has carried out tend to 

 corroborate this view. 



The November Meteors.— At the latter end of this week 

 the earth passes through that stream of meteors which gives us 

 a yearly display on about the 14th of this month. Mr. Denning 

 who IS our chief authority on this subject, and whose admirable 

 memoir on this special swarm should be carefully absorbed tells 

 us that the morning hours of the 14th should be more especially 

 devoted to their observation, although watches should be com- 

 menced a day beforehand and prolonged until the i6th. It is 

 not, however, until the year 1898 that we expect to meet the 

 most dense parts of the swarm, but on former occasions striking 

 displays have been witnessed a year or two previous to the chief 

 one, and this year we hope will be no exception. Let us trust 

 that the weather will not be so unfavourable as it was last 

 November. 



NO. 



[463, VOL. 57] 



.^rrT^^ CONNECTION BETWEEN THE 

 AAji^l?,¥ .^^ ^SOMORPHOUS SALTS 

 AND THE ATOMIC WEIGHT OF THE 

 METALS CONTAINED. 

 JN order to assist in elucidating thequestion of the relationship 

 between the chemical composition of solid substances and 

 the nature of the crystals which they are observed to form, both 

 as regards the exterior geometrical configuration and the interior 

 physical character of such crystals, a series of researches were 

 conimenced by the author six years ago, having for their imme- 

 diate object the exact determination of the differences presented 

 by certain well-defined series of isomorphous salts. The differ- 

 ences in question, due to the diff-erent nature of the inlerchange- 

 al)le chemical elements, belonging to the same family group, 

 which by their mutual replacement give rise to the series, are so 

 small in the case of the morphological constants, that extremely 

 refined methods of investigation are requisite in order to detect 

 and determine them. A large amount of detached data had pre- 

 viously iDeen accumulated in crystallographic literature, but a 

 very small proportion was characterised by the requisite degree 

 of accuracy, and no organised attempt had hitherto been made 

 to investigate any definitely related series of crystallised com- 

 pounds in a sufficiently detailed and accurate manner. The 

 care and precision demanded will be at once apparent when it 

 is pointed out that the use of slightly impure or imperfect 

 crystals, or the occurrence oi slight errors of orientation in 

 grinding out of the crystals the section-plates or prisms requisite 

 for the optical portion of the work, would be sufficient to render 

 the results valueless for the purpose in view. In fact such 

 sources of error have in certain cases been shown by the author 

 during the progress of the work to have led previous observers 

 to conclusions diametrically opposed to the truth. 



It was decided to choose, as most suitable for such a study, 

 certain series containing in their different members the three 

 alkali metals potassium, rubidium, and cresium, on account 

 of the very definite relationship and considerable intervals 

 between their atomic weights, and the extreme electro-positive 

 nature of the group, which latter fact rendered it likely that the 

 differences in question would be here at a maximum. These 

 three metals belong in the strictest sense to the same family 

 group, and their atomic weights are respectively 39, 85 2, and 

 132-8, the atomic weight of rubidium being thus almo.st exactly 

 the mean of the values for potassium and ccesium. The par- 

 ticular salts chosen, on account of the general excellence of their 

 crystals, were the normal sulphates and selenates, and the 

 double sulphates and double selenates which these salts form 

 with the sulphates and selenates of magnesium, zinc, iron, man- 

 ganese, nickel, cobalt, copper, and cadmium. The work on the 

 sulphates, double sulphates, and selenates has at length been 

 completed and presented to the Chemical Society (journ 

 Chem. Soc, 1893, 337; 1894, 628; 1896, 344; 1897, 846), 

 and the investigation of the double selenates is now in hand. 

 The choice of the double salts has proved equally as fortunate as 

 that of the simple salts, inasmuch as the influence of the alkali 

 metal is found to be of a vastly preponderating character com- 

 pared with that of the dyad metal, and hence the eight groups 

 of these salts have furnished so many independent examples of 

 the influence of the atomic weight of the alkali metal. No effort 

 or expense has been spared to render the work absolutely trust- • 

 worthy and of a final character. The goniometers and other 

 optical instruments employed have been without exception the 

 most accurate that could be constructed, and the observations 

 have been more numerously repeated upon different crystals 

 than has ever before been attempted. Moreover, great care has 

 been bestowed upon the preparation of perfectly pure specimens 

 of the salts, no material being accepted which did not yield 

 absolutely satisfactory results upon both spectroscopic and 

 ordinary gravimetric analysis. Besides goniometrical and 

 optical investigation, the work has included exceptionally 

 careful determinations of the relative density of the salts in the 

 crystallised condition, in order to afford data for the calculation 

 of the volume relationships and of the molecular optical con- 

 stants. Moreover, the observations have been extended to 

 other than the ordinary temperatures, in order that the deduc- 

 tions shall not be subject to the objection that they may be 

 simply fortuitous for a particular temperature. 



Before commencing the optical part of the work attention 

 was concentrated upon devising an instrument which should 

 enable a section -plate (slice), or a 60° prism, to be ground out of 



