254 



NATURE 



[July i 6, 1:908 



ani^le. rivet and stay bars, 

 inas. 



steel forginsrs, and steel cast- 



In the Engineering Magazine (vol. xxxv., No. 3) Mr. 

 H. T. Wade gives an illustrated description of an interest- 

 ing exhibition, designed to show the best methods of safe- 

 guarding workmen and of protecting the general public, 

 which was recently held in New York by the American 

 Museum of .Safety Devices and Industrial Hygiene. The 

 exhibition was of great importance in showing that much 

 of the loss of life in industrial operations in the United 

 States is preventable, and that there are already developed 

 methods and appliances that accomplish much in this 

 direction. 



The Zoelly turbine is the youngest of the steam-turbines 

 ■which have risen to any degree of commercial importance, 

 and in view of the fact that it entered a field already 

 occupied by powerful interests and well-established rivals, 

 its progress has been remarkable. Designed by M. Hein- 

 Tich Zoelly, of Zurich, it was first put on the market in 

 1904, and has since then been most energetically developed, 

 particularly on the continent of Europe. It is of the com- 

 pound impulse type, that is, the steam is expanded 

 successively through small ranges of pressure, the velocity 

 acquired during each expansion being utilised by a separate 

 single wheel. Each wheel runs in a compartment by itself, 

 the number of wheels required being determined by the 

 range of expansion through which the turbine has to work, 

 the pressure in each compartment being never less than 

 58 per cent, of that in the previous one. This limitation 

 enables the full expansion at every stage to be obtained 

 -with simple convergent nozzles, which are easier to design 

 and more efficient than the flared nozzles, which become 

 necessary with greater expansion ratios. An exhaustive 

 description of this turbine is given in Engineering of 

 July 3, with dimensioned drawings and reproductions of 

 photographs of the 210 horse-power Zoelly turbine direct- 

 coupled to a centrifugal pump shown by Messrs. Mather 

 and Piatt at the Franco-British Exhibition. 



Messrs. Negretti and Z.imbr.^ have submitted to us 

 'for examination their new prismatic binocular, the 

 " Minim," which they have recently issued. The dis- 

 tinguishing features of the new glass are its compactness, 

 lightness, and small bulk. Its weight is only 10 oz., and 

 it is as small as any other prismatic binocular of the same 

 power, the height being only 3I inches. These points, 

 however, have evidently been attained without any sacrifice 

 of the essential rigidity of an instrument of such high 

 power. The makers state in their specification that, in 

 order to secure this compactness, lightness, and small bulk, 

 in conjunction with so powerful a magnification as eight 

 diameters, it is of course necessary that the lenses and 

 prisms must be small, and that in consequence the light- 

 transmitting power will, under certain conditions, be 

 smaller than with glasses having large lenses. These con- 

 'ditions, however, are not likely to occur often enough to 

 compensate for a conveniently portable instrument, and on 

 an average day the " Minim " gives ample illumination. 

 The size and shape are such that the binocular can be 

 •easily kept in the pocket, and for this purpose it can be 

 supplied in a soft leather case instead of the usual stiff 

 leather sling-case. It is constructed with a well-designed 

 rack focus adjustment on the differential screw principle, 

 giving very easy motion which can be operated by one 

 finger, and which has the additional advantage of not 

 wearing slack with continued use. One eye-lens is 

 separately adjustable for the correction of anisometropia, 

 and both tubes are on the usual swing pivot for adjust- 



XO. 2020., VOL. 78] 



mcnt of pupillary distance. The power of eight diameters 

 inagnification has been chosen after careful consideration 

 as being the best for ordinary requirements, such as tour- 

 ing and every kind of sport ; at the same time, it is not 

 too high for marine worl<, and is about the limit for 

 holding steady without any subsidiary support. We have 1 

 also found it extremely useful for many objects in astro- 

 nomy ; for instance, the views of the half-moon on a cleai: 

 night are magnificent. The general performance of the 

 glass satisfies all of a series of tests on various objects 

 which we have tried. The optical definition is very fine, 

 a pleasing feature being the instantaneous change on either 

 side of the best focus. The images are pleasingly achro- 

 matic. We would urge on users of all prismatic binoculars 

 or high-power telescopes that to get critical definition it is 

 necessary to re-focus whenever the distance of the object 

 being viewed is changed, as these instruments have not 

 the latitude in depth of field to which we are accustomed 

 in the ordinary opera-glass of low power. 



The last number of the Proceedings of the Royal Society 

 of Edinburgh (vol. xxviii., part iv.) includes a paper of 

 forty-three pages on the problem of a spherical gaseous 

 nebula, continuing and completing Lord Kelvin's work 

 upon this subject. In his last paper, a contribution to 

 N.iTL'RE of February 14, 1907, Lord Kelvin directed atten- 

 tion to what he called the curious " Perry theorem," which 

 ought to be called the Ritter theorem, namely, that a 

 spherical mass of gas of which the specific heat ratio is 

 less than I5 must be unstable. W'hat makes a paper of 

 this kind particularly interesting is that Lord Kelvin never 

 satisfied himself with a mere mathematical statement of 

 such a theorem as this ; he always sought out the 

 physical meaning of it. It may be said that the paper 

 gives a complete statement of the development of the past 

 work of Lord Kelvin himself, also of Homer Lane, and of 

 Ritter and Perry. It was left incomplete by the author, and 

 it has been well edited by his secretary, Mr. George Green, 

 who has given much time to the calculation of many 

 useful tables of figures. 



Messrs. Aston .\nd M.ander submit for examination a 

 specimen of the " Compton " slide-rule, which they are 

 selling at nine shillings. As is now universal, the divided 

 surfaces are on white celluloid, and a glass cursor with 

 one cross-line is provided. The radius of the A and D 

 lines are 125 and 250 millimetres respectively, as is usual 

 with rules about 10 inches long. The sine and tangent 

 lines at the back of the slide are graduated from the same 

 end, and in order to be able to read both sines and 

 tangents, or to execute proportions in which one or other 

 come in as factors, without shifting the slide, the slide 

 when reversed is the right way end for end for both 

 at the same time. Of course, as the tangents with this 

 arrangement are read against the D line, they are on 

 twice the scale, and may be read with twice the accuracy. 

 The wood is mahogany, and two celluloid strips are used 

 to face the thin portion of the rule. The two edges are 

 divided, and the inside has the linear divisions continued 

 after the manner of a hat measure. The divisions are 

 fine and accurate, and the working easy and smooth. 



The three articles on the work done at the Physikalisch- 

 Technische Reichsanstalt at Charlottenberg during the year 

 1907, which appeared in the April, May, and June numbers 

 of the Zcitschrift jiir Inslnimentenkunde, have now been 

 issued separately, and form very interesting reading. 

 Sufficient information is given to allow the reader to under- 

 stand the work done and the methods used, and in many 

 cases in which apparatus of a novel kind has been used 

 a figure of it is given. It is scarcely necessary to say 



