158 



KNOWLEDGE & SCIENTIFIC NEWS. 



[July, 1904. 



mile away from the transmitting electrodes. If the field 

 is entirely uniform, then the telephones will show, by the 

 sounds of the tapping in them, that the direction of the 

 lines of How of the current is approximately in accord- 

 ance with the theoretical diagrams as shown in text 

 books. 



Now we come to the (juestion of the variations from 

 the normal, caused by underground deposits of metalli- 

 ferous bodies. Lodes are electrically divided into two 

 classes, those w-hich are better conductors than the 

 enclosing rock, and those which are, comparatively 

 speaking, insulators. A good conducting lode changes 

 the shape and intensity of the normal field in a remark- 

 able manner — elongating it in the direction of the strike. 

 Waves passing into the lode at great depths are brought 

 up to the surface. Hence, over the apex of the lode 

 there is a concentration of energy and a correspondmg 

 increase of the sounds in the telephones when in the 

 neighbourhood of the lode. In this way the position of 

 the lode is easily ascertained, and, on exploring with the 

 receiving electrodes further and further away, no sounds 

 are heard whatever, except over the path of the lode. 

 By moving the electrodes, a point is found where the 

 sound suddenly ceases in some cases, but is again audible 

 on moving the electrodes a little further. This point of 

 equipotential and consequent silence occurs when the 

 electrodes are so placed that the apex of the lode is mid- 

 way between them. Absolute silence is not invariably 

 attained, but in the case of conducting lodes, a diminution 

 of sound always occurs. If the operator is nearer to the 

 transmitting base and is receiving some of the normal 

 waves which are travelling on and near the surface at an 

 angle to the direction of the lode's strike a cross field is 

 observed when the lode is between the electrodes, and 

 the telephones give broken and discordant sounds. With 

 lodes which act as insulating bodies, the field is never 

 elongated, but possesses its normal shape. The waves, 

 on encountering the lode, are brought to the surface of the 

 -ground on account of their inability to pass through, 

 and, consequently, are all concentrated in the space 

 between the apex of the lode and the earth's surface. 

 When the telephone electrodes — being moved across the 

 field at right angles to the direction in which it is ex- 

 pected the ore bodies strike — arrive at a point over a 

 lode of this kind the increase in sound is sudden and 

 intense, as might be expected when we consider the 

 great depths from which the insulating body causes the 

 waves to be brought. 



There are many other ways of examining and testing 

 the lie of veins and lodes; and the skilled investigator is 

 able, by a suitable restriction of the electric field and by 

 adjustment of the potential of the transmitting current, to 

 apply tests for the depth of the lode. Much has probably 

 yet to be done in elaborating the -possibilities of this 

 method, and in simplifying or codifying its applications, so 

 as to render it accessible in ordinary use ; but of its use 

 and of its interest no doubt need be entertained. 



-rrfe-^r^ 



The Japanese explosive, Slilmosc, has been said to be 

 more powerful than oil her dynamite or guncotton. 

 .Shimose docs not explode on percussion, or by fire, 

 and is not injured by wctling. When it is exploded, 

 by a chartje of fulminite, it te.irs a hole gfreator than 

 would result from the use of a similar quantity of 

 dynamite, and, unlike th.it substance, its force is equally 

 exerted in all directions. 



ASTRONOMICAL. 



The Solar Parallax. 



At the last meeting of the Royal Astronomical Society on 

 June 10, Mr. A. K. Hiaks read a paper on the determination of 

 the Solar parallax from the measurement of photographs of the 

 minor planet Eros, taken at the Cambridge Observatory, and 

 at several other co-operating observatories. The value ob- 

 tained agreed very closely indeed with that secured several 

 years ago by Sir David Gill from observations of the three 

 minor planets — \'ictoria, Iris, and Sappho ; Mr. Hinks getting 

 8"796, as against Sir David Gill's S"-So2. -At the Academie 

 des Sciences of Paris on June 6. M. Bouquet de la Grye gave 

 the result of the measurement of the photographs of the transit 

 of \"enus, 1SS2, obtained by the French expeditions. These 

 gave values varying from S"'7S6 to S"'7y2. 

 * * ■* 



An Interesting Variable Star. 



Xumbcr 6760 ot ChdiiJIer's Catalogue of X'ariable Stars is a 

 4th magnitude star, bearing the name of Kappa Pavonis. Its 

 variability was discovered by Dr. Thome in 1871, and it has 

 been the subject of a very careful scrutiny during the last 

 thirteen years by Dr. A. \V. Roberts, of Lovedale, South 

 Africa. The period of variation is about nine days, and the 

 range from magnitude 4 to magnitude 5-5. The period of 

 increase is slightly shorter than the period of decline — 

 M — m = 4-71 days, whilst m — M = 4-38 days; but when 

 all the observations are brought together and compared with 

 the ephemeris, it is seen at once that there is a small syste- 

 matic v.'iriation in the length of the period — a variation which 

 goes through all its phases in the course of eight years. This 

 would be explained if we regarded the variable as travelling in 

 an orbit seventy times as large as that of the earth, in a period 

 of eight years, implying that it was revolving round an invisible 

 primary of a mass 5000 times as great as that of the sun. It 

 is, of course, possible that this secular variation may be 

 accounted for in other ways, and may even be purely obser- 

 vational in character; but it suggests that the star should 

 make a very promising subject for the most careful heHometer 

 and spectroscopic observations. 



■if -jr * 



The Stars of Secchi's Third Type. 



The distinguishing feature of the spectra of these stars — 

 '■ Aiitarian '' stars, as Sir Norman Lockyer calls them, after one 

 of the brightest examples of the type — is the system of seem- 

 ingly dark flutings. sharp towards the violet, and shadirg off 

 towards the red end of the spectrum. Until quite recently 

 the origin of these flutings has remained without any ^a'is- 

 factory explanation, and indeed, the question has been debated 

 as to whether the spectrum should not be regarded as one 

 consisting parily of bright flutings fading towards the \iolet, 

 rather than as one consisting wholly of absorption flutings 

 fading towards the red. Professor .A. F'owler, of l!.e Royal 

 College of Science, South Kensington, in a papt r recently 

 communicated to the Royal Society, appears to have given a 

 satisfactory solution to this long-standing problem. He finds 

 that the flutings are truly absorption eff'ects, ai d that they 

 correspond within the possible limits of en or with the 

 flutin,gs of titanium. The flutings in question co:ne out in the 

 arc spectrum, if a liberal supply of titanium oxide be used 

 with a very long arc. As yet Professor Fowler has not been 

 able to decide completely whether the flutings are due to the 

 vapour of titanium itself or tothat of itsoxide. It is interesting 

 to note, especially in view of the correfpondences which 

 Professor Hale has found in stars of the fourth type to the 

 lines typical of the spectra of sunspots, that Miss Gierke last 

 year, in her book " Problems in Astrophysics," definitely 



