NA TURE 



[May 13, 1909 



La Nature for April 24 contains an account of tlie ex- 

 periments and measurements which have been made to 

 discover what was the cause of the notoriously bad 

 acoustical properties of the large hall of the Trocad^ro at 

 Paris. The work has led to several valuable conclusions 

 as to the effect of a sound reaching the ear by two paths 

 which differ in length by various amounts up to 34 metres. 

 One of these is embodied in the statement that, for good 

 audition, surfaces far from the audience must be absorbent, 

 •while surfaces near them must be reflecting. 



It will be remembered that two years ago the well- 

 Tcnown " pleochroic haloes " observed in rock sections were 

 shewn to be due to the radio-activity of the inclusion 

 round which the halo occurs. The point was brought out 

 about the same time by Prof. O. Mijgge in Germany and 

 by Prof. Joly in this country. The former author now 

 contributes further observations on the action of radium 

 in producing these effects on a variety of minerals. His 

 results will be found in the Centralhlatt fur Mineralogie 

 ■0909, p. 65). 



Mr. C. Baker, of 244 High Holborn, VJ.C, has sub- 

 "mittcd to us two microscope objectives of a new formula 

 which he has recently placed on the market. They are 

 (i) a one-sixth inch numerical aperture, 0.75 ; (2) a one- 

 twelfth inch numerical aperture, 1-30. The former has 

 approximately a working distance of one millimetre, 

 •which for its focal length is considerable, and is intended 

 for use with thicker cover glasses or with a hjemocyto- 

 meter. The one-twelfth inch objective is particularly suited 

 for bacteriological work, and, considering that it has a 

 large field, its definition is excellent. We have tried these 

 lenses both visually and photographically, and can find 

 little fault with them. They are of the type that most 

 English makers have recently introduced, and are intended 

 to meet the need for cheap lenses for students' purposes 

 and for ordinary use in the commercial applications of 

 the microscope. The prices of these lenses are thirty 

 shillings and five pounds respectively, and it is somewhat 

 reassuring to find that English firms are making a deter- 

 mined effort to meet the severe Continental competition in 

 the cheaper class of microscope apparatus, by introducing 

 lenses of such a high order for so reasonable a price. 

 Photographically, both these lenses are most satisfactory, 

 and, if used in conjunction with a light yellow screen 

 which cuts out the blue-violet portion of the spectrum, the 

 results to be obtained with them are excellent. In common 

 with most lenses of this type, their focal length is slightly 

 shorter than marked, but this but little detracts "from 

 their performance. 



The new White Star liner Laurcntic left on her first 

 voyage to Canada on April 29. The performance of this 

 vessel, built by Messrs. Harland and Wolff, of Belfast, 

 will be looked for with interest, as she is the first Atlantic 

 liner to be fitted with a combination of reciprocating and 

 turbine machinery. Meanwhile, we note from an article 

 in Engineering of April 30 that the vessel has a length 

 of 565 feet 6 inches over all, beam 67 feet 3 inches, and 

 depth, moulded, 45 feet 6 inches ; the displacement at 

 service draught is about 20,000 tons. The idea of the 

 combination of machinery is to utilise in the turbine the 

 remaining heat energy in the exhaust steam from recipro- 

 cating engines, which is generally at a pressure not less 

 than 10 lb. per square inch absolute. The Parsons steam 

 turbine enables such steam to be expanded economically 

 to a very low absolute pressure. In the Laurentic the 

 reciprocating engines are of the triple-expansion type, with 

 NO. 2063, VOL. 80] 



four cylinders to ensure perfect balancing. There are 

 twin reciprocating sets, the low-pressure Parsons turbine 

 being placed in the centre of the ship and abaft the main 

 engines, giving three propeller shafts. Arrangements are 

 provided for throwing the turbine out of action for all 

 manoeuvring, the reciprocating engines then passing their 

 exhaust steam direct to the condenser. The experience 

 derived from this vessel should be of service in proportion- 

 ing the machinery of the two 45,000-ton White Star liners 

 now being built in Belfast. 



OUR ASTRONOMICAL COLUMN. 



Mercury as an Evening Star. — In the comparatively 

 clear evening skies of the past week, the planet Mercury 

 has not been ditTicult to locate when one knew the direc- 

 tion in which to look for it. At present it is in the con- 

 stellation Taurus, to the south-west of /3 Tauri, and sets 

 about two hours after sunset. 



The greatest eastern elongation takes place on May 20, 

 but the planet is better seen some days before, rather than 

 after, an elongation occurring in the spring. At 8.30 p.m. 

 on Saturday last, May 8, it was easily found with opera- 

 glasses whilst some four or five degrees from the horizon, 

 and then watched for some time with the naked eye. 



The Present Solar Activity. — A large group of spots 

 was seen coming round the eastern limb of the sun on 

 Friday last. May 7, and was in full view on Saturday, 

 when it was seen to consist of two moderately large spots 

 with several smaller ones, and to cover a fairly extensive 

 area. On Sunday the group was visible to the naked eye, 

 shielded by a piece of smoked glass, whilst with a pair 

 of opera-glasses (X3), similarly shielded, it was quite a 

 prominent object. 



Spectroscopic observations made at the Solar Physics 

 Observatory by Mr. W. E. Rolston on Saturday showed 

 that the dark t), (helium) line was to be seen quite marked 

 in the different inter-umbral areas and beyond the group. 



The Intka-Mercurial Planet Problem. — As reported in 

 our discussion of the results obtained bv the Lick-Crocker 

 eclipse expedition to Flint Island (Nature, No. 2038, vol. 

 Ixxix., p. 70, November 19, 1908), Prof. Campbell con- 

 siders that the negative results obtained at successive 

 eclipses in the search for a possible intra-Mercurial planet 

 demonstrate that no such planet exists as would account 

 for the anomalies in the motion of Mercury. 



In the May number of the Popular Science Monthly 

 (vol. Ixxiv., No. 5, p. 494) he now gives a most interest- 

 ing popular account of the search for the hypothetical 

 planet, and the means whereby its existence has been 

 disproved. 



In closing this account. Prof. Campbell refers favour- 

 ably to Prof. Seeliger's recently published conclusions that 

 the Mercury anomalies may be accounted for by the action 

 of the material which gives rise to the zodiacal light, and 

 shows that the figures calculated by Seeliger agree, within 

 the probable errors, with the observed values, as reduced 

 by Newcomb, of the perturbations of Mercury, Venus, the 

 earth, and Mars. 



The Lick Observatory search is fully discussed, in 

 Bulletin No. 152, by Dr. Perrine, who points out that, 

 whilst small bodies mav vet be discovered near the sun, 

 the eclipse plates show that no planet of the eighth magni- 

 tude was photographed. Such a planet would hardly 

 exceed twenty or thirty miles in diameter, and it would 

 require about a million such bodies to account for the 

 outstanding Mercury perturbations. 



Partial Eclipse of the Sun in Canada. — From Dr. 

 Downing we have received particulars of the partial phase 

 of the solar eclipse of June 17 as visible at the Canadian 

 observatories, .^t Ottawa the greatest phase (0-601) will 

 occur at 7h. 43m. (standard time, 5h. \V.), and the sun 

 will set partially eclipsed at 7h. 50m. ; first contact will 

 occur at 6h. 52m. At Toronto the times will be : — first 

 contact, 6h. S7m. ; greatest phase (0.540), 7h. 48m. ; sun- 

 set, 8h. om. In each case the sun's altitude at first 

 contact will be approximately 9°. 



