April i, 1909] 



NATURE 



141 



magnetic work has an importance attached to it in the 

 United States to which there is hardly a parallel elsewhere. 



A TAPER on the construction and wear of roads, by Mr. 

 H. A. R. Mallock, F.R.S., was read before the Institu- 

 tion of Civil Engineers on March 23. The subject was 

 considered from a theoretical point of view with regard to 

 the foundation of the road, its surface, and the character 

 of the traffic. It was suggested that roads with a hollow 

 cross-section, drained by a central gutter covered by a 

 continuous grating, would be worthy of trial, as tending 

 to prevent the accumulation of mud and water close to the 

 footways, and as giving the greatest facilities for keeping 

 the whole of the roadway clean. The origin of dust and 

 mud on roads is imputed almost entirely to the grinding 

 and crushing action of iron tyres and iron horseshoes. The 

 conclusion drawn from the whole of the evidence is that 

 the chief enemies of good roads are iron tyres and iron- 

 shod horses, or, indeed, any forms of traction which cause 

 very intense local pressure on the road surface. The view 

 was expressed that with soft tyres the wear on any good 

 road is extremely small, and with pneumatic tyres still less, 

 but that so long as iron tyres and iron-shod horses are 

 used for traction, the best means of preserving a clean 

 and unbroken road surface is to be found either in the 

 applications of tar (many of which have already been made 

 with considerable success), or in some other method which 

 will give the same large limits of elasticity and rupture 

 to the upper layer of road material. For roads used 

 exclusively by soft tyres there is a far wider choice of 

 suitable road material than where the surface is exposed 

 to very intense pressure. 



.A SECOND edition of Dr. M. .Abraham's " Elektro- 

 magnetische Theorie der Strahlung " has been published 

 by the firm of B. G. Teubner, of Leipzig and Berlin. 

 This work is the second volume of the " Theorie der 

 Elektrizitat," reviewed irt our issue for August 15, 1907 

 (vol. Ixxvi., p. 377). The price of the present part is 

 10 marks. 



We note with interest and satisfaction the publication 

 of German editions of two well-known works of science 

 originally- published in English. The first is " Habit and 

 Instinct," by Prof. Lloyd Morgan, F.R.S., which has 

 been translated by Maria Semon, and issued by the firm 

 of B. G. Teubner, of Leipzig and Berlin, at the price of 

 5 marks. The second is Prof. .Alexander Smith's " Intro- 

 duction to General Inorganic Chemistry," translated by 

 Dr. Ernst Stern, and published by the firm of G. Braun, 

 of Karlsruhe. 



OVR ASTRONOMICAL COLUMN. 

 Astronomical Occurrences in April : — 

 April I. 22h. Tupiter in conjunction with the Moon (Jupiter 

 3''45'S.). 



2. 22h. Saturn in conjunction with the Sun. 



3. gh. 5501. to iih. 5m. Moon occults e Virginis (mag. 



4-2). 

 10. gh. 8ni. to I2h. 3401. Transit of Jupiter's Satellite 



III. (Ganymede). 



,, I5h. 52m. to i6h. 32m. Moon occults /' Ophiuchi 



(mag. 4-3). 

 13. igh. Mars in conjunction with the Moon (Mars 



2° 29' N. ). 

 15. loh. 30m. to 14'). 46m. Transit of Jupiter's Sa'ellite 



IV. (Callistoi. 



19. 9h. 43m. Minimum of Algol {$ Persei). 

 19-22. Epoch of Lyrid meteors. (Radiant 27i°-)-33°.) 

 21. Venus. Apparent diameter 9 ""8. 



NO. 2057, VOL. 80] 



The RoT.'iTioN of the Sun. — In a paper appearing in- 

 the March number of the Astrophysical Journal (vol. xxix.. 

 No. 2, p. no) Prof. W. S. .Adams gives and discusses the- 

 results obtained during igo8 in the spcctroscopical investi- 

 gation of the sun's rotational velocities. In general, these 

 results agree closely with those obtained during the 1906-7 

 investigation, although for latitudes greater than 50° larger 

 values are now obtained for the velocity; there is no- 

 evidence, however, of the existence of a variation of the 

 rate of rotation. Lines of lanthanum and of cyanogen are 

 again found to give low values, as are also two ■ 

 " enhanced " lines investigated. On the other hand, 

 certain lines of manganese and iron indicate high veloci- 

 ties. In general, such abnormal behaviour becomes more 

 marked in the higher latitudes. 



The present results were derived from spectrograms 

 taken with the tower telescope and the 30-feet spectro- 

 scope, and show a marked increase of probable accuracy 

 over those obtained with the smaller equipment in 1906-7- 

 Thev also show that Faye's equation for the rotation holds 

 quite good up to within 10° of the poles. Special plates 

 taken with solar vortices in the field show that the vortices 

 may introduce variations of such magnitude as to invalidate - 

 any conclusion normally derived from the measures. 



Special studies were also made of the behaviour of th& 

 calcium line at X 4227 and of the Ha line, and it was 

 found that both give high rotational velocities ■, such 

 abnormalities are explained by the greater height reached' 

 bv the matter producing these lines. The former line was 

 found to be indubitably double, although the separation 

 of the components is extremely small. The study of Htt 

 gave some very interesting results, among which we may 

 mention that at different distances from the limb this line 

 indicates very different velocities; it also shows only a 

 slight equatorial acceleration. 



Common Motions of the Principal Urs.e Majoris 

 Stars. — -A number of investigators have discovered evideiice 

 of a probable physical connection between the seven prin- 

 cipal stars of the constellation Ursa Major, and in - 

 Nos. 4313-4 of the Astronomische Nachricliten Dr. Luden- 

 dorff again discusses the question on the basis of radial 

 velocities determined at Potsdam. 



The radial velocities of ;3, e, and f UrsEe Majoris were- 

 investigated. In the case of p, the measures indicate a 

 variable velocity with a period of about 27-16 days. The 

 absolute values' found for e can only be looked upon as 

 approximate, .but they indicate a variability of restricted 

 range and long period', the variation being between -8 km. 

 and -iS km., with a period of about 2-1 years. The 

 centre of gravity of the system of f Ursee Majoris is shown • 

 to have a large' range (269 km.) of velocity, with a period 

 of 20-536 davs. 



Considering together the proper motions and parallaxes 

 of the seven stars, it is found that there are probably two 

 connected systems, system i. including /3, y 5, e, and f, 

 and system ii. including a and 7;, both of which have 

 approximatelv the same parallax and the same velocity 

 l-elativo to the sun, but the angle between the directions 

 of the two systems is about 101°. 



The Surface of Rotating Mercury as a Reflecting 

 Telescope. — Having made a striking series of experiments 

 on the possibilities of the paraboloidal surface of rotating 

 mercury as a reflecting telescope. Prof. R. W. Wood' 

 describes and illustrates his results in No. 2, vol. xxix., 

 of the Astrophysical Journal (p. 164, March). 



Prof. 'Wood' succeeded, by very finely adjusting the- 

 motion of his rotating tank, in producing mercury 

 surfaces on which the disturbances were negligible, and' 

 for which a constancy of focus could be maintained for 

 some time. .Although the experiments appear, at first 

 glance, to be merelv of theoretical interest. Prof. Wood is 

 so gratified with the results that he suggests methods 

 whereby results of practical interest might be obtained. 

 One of these is the possibility of taking casts, in some 

 easilv fusible material, of sufficient rigidity when solidified' 

 to bear electrotypes being made from it. These electro- 

 tvpes, suitably mounted and silvered, might then be used 

 in reflecting telescopes. 



Photographs of the Earthshine on the Moon. — Two 

 excellent photographs, showing the greater part of the 



