June 26, 191 3] 



NATURE 



435 



National Argentine < Hiservatorv in Cordoba, presents 

 a catalogue of 5791 stars. The work is the outcome 

 of 28,718 observations made with the 5-in. Repsold 

 meridian circle during the six years 1885-90. The 

 observations are of a general nature over the southern 

 sky, and form a continuation of the general catalogue. 

 Auwers's list of 303 fundamental stars was observed 

 in 1889 by Prof. Updegraff, and the results are 

 included in this catalogue. There is also included 

 a list of sixty-three comparison stars for the minor 

 planet Victoria, observed in 1889 by Prof. Updegraff, 

 and this is given separately, in addition to being 

 included in the regular catalogue. There was no 

 unusual change or condition of the meridian circle 

 during the period mentioned, so far as is known, and 

 the reductions were made in precisely the same 

 manner and with the same system of constants as 

 in the general catalogue. The catalogue also in- 

 cludes the results of a comparison with Boss's Pre- 

 liminary General Catalogue of the stars common to 

 both. 



The Milky Way and the Distribution of Stars 

 with Peculiar Spectra. — The distribution with refer- 

 ence to the galaxy of the many stars having peculiar 

 spectra classed by the late Mrs. Fleming has been 

 analysed by Mr. T. E. Espin, and the results appear 

 in the March-April number of the Journal of the 

 Royal Astronomical Society. The distribution 

 evidence suggests that the order A, F, G, K, M of 

 the Harvard classification of stellar spectra requires 

 rearranging thus, A, G, M, K, F. The author makes 

 some interesting speculations on the structure of the 

 galactic system. 



THE MICROSCOPE SUBSTAGE AND ITS 

 ADJUSTMENTS. 



THERE are one or two points, particularly in the 

 substage arrangements, which are distinct and 

 ( haracteristic of English and Continental microscopes. 

 In the English instrument of any pretensions 

 it has always been the custom to provide a centring 

 substage, and this carries both the optical portion of 

 the substage condenser and the iris diaphragm. It has 

 to be assumed, therefore, that the iris diaphragm is 

 centred permanently and accurately to the optic axis 

 of the substage condenser, its perfection therefore 

 depending on the extent to which this assumption is 

 justified. 



In the case of the Continental microscope, where a 

 centring substage condenser is provided, it is 

 mounted so that the optical part is centred independ- 

 ently of the iris diaphragm, the latter, in fact, being 

 mounted below the substage condenser and having 

 certain adjustments which are in no way connected 

 with the centring arrangement. It therefore follows 

 that in the Continental type the iris diaphragm may 

 be, and indeed often is, permanently out of centre 

 with the optic axis of the objective. The substage 

 condenser has therefore to be centred in relation to 

 two axes, the centre of the iris diaphragm and the 

 optic axis of the objective, which themselves are not 

 in exact alignment. It is obvious that under such 

 conditions the provision and use of a centring appli- 

 ance for the adjustment of the optical part of the 

 condenser will never result in correct alignment of the 

 various parts. With the object of overcoming this 

 defect, at least in part, some of the better Continental 

 models have been provided with an independent ad- 

 justment to enable the mechanic to centre the con- 

 denser to the optic axis, after he has centred the iris 

 diaphragm. The condenser is mounted in a ring 

 provided with three screws, the setting of which 

 admits of the optical part of the condenser being 

 NO. 2278, VOL. 91] 



centred, but this is, of course, not an adjustment of 

 which the average user would care to avail himself. 

 In the English arrangement, where the iris dia- 

 phragm is correctly centred to the substage condenser, 

 centration of the whole substage fitting results in 

 correct alignment with the remainder of the optical 

 system of the microscope. 



For the most critical work, therefore, it would 

 appear that the English method is to be preferred. 

 On the other hand, where a microscope is being used 

 for laboratory work, and is only occasionally being used 

 for the testing of objectives or for critical pur- 

 poses, there is no doubt that the Continental type has 

 much to recommend it. The fact that the iris dia- 

 phragm may be contracted to any desired degree, and 

 may then be shifted laterally so that oblique illumina- 

 tion in any azimuth and in any zone of the field of 

 view can be obtained at will, is a great convenience, 

 and for anything like rapid testing of objectives is 

 almost essential. 



In the English stand it becomes necessary to pro- 

 vide stops of various sizes and shapes, which can be 

 placed at the back of the substage condenser, to enable 

 oblique illumination to be obtained in any desired 

 manner. 



Where absolute accuracy is required it would appear 

 that an arrangement in which both substage con- 

 denser and iris diaphragm are capable of independent 

 centration might be a desideratum. In such a case 

 the iris diaphragm would be centred first, and then 

 the optical part of the substage condenser introduced, 

 and that centred independently. By this means the 

 iris diaphragm, the substage condenser, and the ob- 

 jective would be in exact alignment, and the arrange- 

 ment would be such that work of the most critical 

 character could be carried out. It must be admitted, 

 however, that the conditions under which such a 

 method would become necessary rarely, if ever, arise, 

 so that a well-made instrument provided with the 

 Continental type of substage, in which the iris 

 diaphragm may be decentred, is a very desLable 

 adjunct to any good microscope. 



As an indication of the perhaps unnecessary elabora- 

 tion that has obtained in English stands, one may 

 mention the provision of a fine adjustment to the sub- 

 stage condenser._ It is difficult to conceive under what 

 conditions this becomes necessary. A well-made rack- 

 work should provide all the accuracy of adjustment 

 that is required. If it does not it either implies that 

 the mechanical construction of the microscope leaves 

 something to be desired, or that the user has not 

 acquired the necessary manipulative skill to focus his 

 substage condenser with sufficient accuracy, the latter 

 alternative being the more probable. 



AUSTRALIAN METEOROLOGY. 



'THE Australian Meteorological Bureau has issued 

 J- a series of interesting maps showing the normal 

 distribution of temperature and rainfall over the 

 Australian continent. The variety of climate which 

 Australia offers is well illustrated by these charts. 

 The mean summer temperature of the south coast of 

 Victoria (between 6o° and 65 F. for January) is about 

 the same as the mean summer temperature of London, 

 while 400 miles to the north the heat is tropical, with 

 a mean temperature of more than 80° F., increasing- 

 to more than S5 F. in the greater part of the north- 

 west and central regions. The trend of the isotherms 

 near the coasts shows the usual oceanic effect ; thev 

 bend southwards in the winter and northwards in the 

 summer in passing from continent to ocean. The 

 isotherms are closest together near the southern coast 

 in summer and near the northern coast in winter. 



