July 7, 1910] 



NATURE 



19 



tanks and all connections being, if deemed necessary by 

 the surveyor, tested to the same pressure as when new. 

 The screw-shaft is to be drawn at intervals of not more 

 than two years. 



In directing attention to the diversity of published results 

 of compressive tests on cubes of concrete, the Builder for 

 June 18 suggests that the explanation is to be found in the 

 different methods and diflerent pressures used in ramming 

 the concrete into the test moulds. We may add to this 

 explanation the fact that variation in the water used in 

 mixing the concrete under test is a most important factor, 

 influencing both the ramming pressure required and also 

 the strength of the resulting specimen. Our contemporary 

 suggests that an appliance such as is used in the Charlotten- 

 burg laboratory might be adopted in this country. In 

 this appliance a ram is lifted by gearing and released by 

 a cam, the arrangement being such that the ram always 

 falls from the same height. After each blow the ram is 

 automatically moved for a short distance in a direction 

 parallel to the axis of the actuating wheel, while the 

 mould is moved perpendicularly to the same axis. The 

 effect is to ensure uniform ramming of the whole. It is 

 stated that the experience at Charloltenburg shows the 

 resistance of test blocks so prepared to be very uniform 

 for concrete of given composition. 



OUR ASTRONOMICAL COLUMN. 



Astronomical Occurrenxes in Ji'ly : — 

 July 12. I4h. Ilm. Jupiter in conjunction with the Moon 

 (Jupiler 2" 5S S. ). 



15. Mercury. Illuminated portion of disc = 0'978, Venus 



= 0-813. 



16. loh. 39m. Minimum of Algol (S Persei). 



19. Saturn. Major axis of outer ring = 39'96", minor 



axis=i2-35". 

 21. 9h. 6m. Uianus in conjunction with Moon (Uranus 



3° 44' N. ,'. 

 27. 6h. 29m. to gh. 9m. Transit of Jupiter's Sat. III. 



(Ganymede). 

 27-31. Meteors abundant from Perseus and Aquarius. 



• Halley's Comet. — A number of observations, generally 

 confirmatory of those already noted in these columns, are 

 recorded in No. 4421 of the Astronomische Nachrichten. 

 Dr. Wolf gives a sketch of the tail showing its position, 

 with regard to the surrounding stars, and its form as 

 shown on a photograph taken on May 12 at I4h. 15m., 

 Kbuigstuhl M.T. This shows that a straight, narrow tail 

 extended from the head to just south of 70 Pegasi, and 

 from there to the end was bounded by two faint clouds of 

 cometary matter, too faint to be seen visually. The out- 

 line of the northern cloud was very irregular, and departed 

 considerably from that of the visual tail, and in any dis- 

 cussion as to whether the earth passed through any mass 

 of cometary material these abnormal extensions must be 

 taken into consideration. 



Prof. Seeliger reports that, at Munich, careful observa- 

 tions failed to reveal any trace of the comet's head or 

 nucleus during its passage across the solar disc, nor were 

 any magnetic or electrical phenomena recorded which could 

 be, with certainty, attributed to the comet. So many 

 observers report the non-detection of the nucleus that it 

 must now be taken as fairly certain that the material of 

 which the head and nucleus are composed is too tenuous 

 to interfere, effectively, with the passage of light. 



M. Eginitis gives further details as to observations at 

 Athens Observatory, and directs special attention to the 

 pecuUar shape presented by the comet on the evening of 

 May 20. The appearance was very similar to that of a 

 crescent moon, with a very bright condensation at the 

 centre of the convex arc, and no extended tail was seen ; 

 such a form might be explained by assuming that the axis 

 of the- tail was nearly in the line of sight. This would 

 also explain the apparent anomaly of the slight tail being 

 turned towards the sun if one supposes that the curvature 

 NO. 2123, VOL. 84] 



was sufficiently great ; in this case, the passage of the 

 earth through that part of the tail extending to its orbit 

 would have been delayed some forty to si.xty hours, and 

 it appears to be probable, if these observations of May 20 

 are verified, that a passage did actually take place. 



M. Comas Sola gives drawings showing the definite 

 duplication of the nucleus on June 2, and the appearance 

 of four or five separate condensations, globes, on June 4. 



In an interesting communication to the Comples renins 

 (No. 26, June 27, p. 1732), M. Nordmann discusses the 

 amount and the nature of the light emitted by the comet, 

 as observed with his colour-screen photometer. He finds 

 that on three dates of observation, April 25, May 15 and 

 23, the nucleus contributed only about one thirty-seventh 

 of the total light emitted by the head. By comparing his 

 values with the observed diameters of the nucleus and 

 coma, respectively, he deduces that towards May 15 the 

 mean intrinsic light of the nucleus was about ' nineteen 

 times that of the visible part of the coma. Taking the 

 theoretical increase of light of a comet as varying in the 

 ratio i/r^A^, and comparing his observed with the calculated 

 values, -M. Nordmann finds that between April 25 and 

 May 23 the augmentation of the brilliancy of the nucleus 

 was much less than provided for by the theory. Finallv, 

 by the employment of his colour-screen method', M. Nord- 

 mann found that the distribution of energy in the spectrum 

 of the nucleus was very similar to the distribution in the 

 so'ar spectrum, and hence he concludes that the light of 

 the nucleus is almost exclusively, if not entirely, reflected 

 sunlight. 



Mr. Leach, Malta, reports that, after finding the comet 

 so faintly distinguishable on June 14, he gave up all hope 

 of seeing it again. On June 25, however, he saw it quite 

 clearly at 9 p.m., and was able to follow it each evening 

 until the day of writing, June 30; with field-glasses, a tail 

 2° or 3° in length was clearly visible. 



Ephemeris for Comet 1910a. — In No. 4422 of the Astro- 

 nomische Nachrichten Prof. Kobold gives a continuation 

 of his ephemeris for comet 1910a. The position is chang- 

 ing very slowly, and for July 7 is 2ih. 40-sm., -1-33° 21-4'; 

 an observation by Prof. Barnard on June 7 gave a correc- 

 tion of -H7S., -t-i-6', and showed the magnitude to be 

 about i6-o. 



Photographs of Morehouse's Comet. — From the Tokio 

 Observatory we have received part vi., vol. iii., of the 

 Annnles, in which are reproduced nearly fifty excellent 

 photographs of Morehouse's comet, 1908c. Messrs. 

 Hirayama and Toda briefly describe the separate photo- 

 graphs, and discuss the remarkable changes which took 

 place in the comet's tail. By comparing their results with 

 those obtained at the Yerkes and Heidelberg Observatories, 

 they find that between October i and 2 a recognised de- 

 tached mass, at a mean distance of 2-4° from the head, 

 was receding at an hourly rate of 8-5' ; other values are : — 

 October 15, 1° from head, northern mass 3-1', southern 

 mass 3-4', per hour; October 15-16, 1-4° from head, 3-1' 

 per hour. As is pointed out, the accumulation of such data 

 will serve to determine the nature of the repulsive force. 

 .■\ discussion of the photographs also discloses that on 

 November 13, 14, 15, and 16, the outer streamers of the 

 tail appeared to change in phase, predominating south- 

 wards on November 13 and 15, and northwards on 

 November 14 and 16. This might be ascribed to a rotation 

 of the head, with a period of forty-eight hours, but further 

 discussion is necessary to estabhsh this ; in any case, the 

 photographs show that if such a rotation existed it was not 

 uniform throughout the tail, for the outer and inner 

 streamers did not rotate with the same angular velocity. 



The Determination of Position near the Poles. — .\s 

 an excerpt from the Geographical Journal for March, we 

 have received a copy of a paper by Mr. Hinks deaUng 

 with the methods of determining an observer's position 

 when near the poles. Mr. Hinks suggests that a theo- 

 dolite, say a 3-inch, read on both faces, would prove the 

 most suitable instrument, and then proposes a modification 

 of Sumner's method for the reduction of the observations. 

 Two observations of the sun at two different known 

 G.M.T. 's give two circles of equal altitude which inter- 

 sect at the observer's position ; a simple graphical method 

 may be used for the reduction. A most interesting dis- 

 cussion, by well-known explorers, followed the reading of 



