November 14, 1907J 



NATURE 



31 



being required for its measurement. The radium present 

 in this case was about i/ioo that contained in the sample 

 nine }ears old. 



It was not to be supposed that an insufficient degree 

 of purity was the cause of the large amount of radium in 

 the old sample, nor is it probable that thorium itself 

 slowly decomposes into radium. I therefore considered 

 that in the technical preparation of thorium an active sub- 

 stance is separated with the latter, and in turn decomposes 

 into radium ; it is probably the direct parent substance of 

 radium, for which search has been recently made. In 

 order to test this view, an attempt was made to show 

 the increase in the amount of radium in a solution of 

 thorium ; loo grams of freshly prepared thorium nitrate 

 was examined, the quantity of radium being ascertained. 

 The amount of emanation collected after four days was 

 used for calculating the equilibrium amount, which is 

 reached after about a month. On August 17 the flaslc 

 was sealed, and again tested on October 10; the amount 

 was double as great as in the previous test. 



Forty grams of thorium nitrate prepared at the end 

 of April was examined in the same way and left during 

 the vacation. In this case also there was a marked 

 mcr?ase in the amount of radium. 



Fifty grams of thorium nitrate made in June, 1907, 

 was precipitated from acid solution with oxalic acid. In 

 the filtrate the quantity of radium was determined, the 

 same being also done in October. In each case the same 

 result was obtained. The parent substance of radium had 

 therefore been precipitated witli the thorium. By mistake, 

 the precipitated material was mixed with other thorium 

 preparations, and could not, therefore, be further investi- 

 gated. 



.About I mg. of radio-thorium (activity about 100,000) 

 was freed as far as possible from radium (the small 

 nniount retained being determined) and sealed up on 

 .August 15. The solution on October 14 gave the same 

 amount of radium emanation as before. The radio- 

 thorium was prepared from thorianite by means of barium 

 sulphate, and should not. therefore, have contained the 

 parent substance of radium, as, indeed, was actually found 

 to be the case. 



Knowing the proportion of uranium and thorium in 

 monazite sand, and assuming that all the thorium and the 

 whole of the parent substance of radium are separated 

 during the extraction of thorium, the life of radium can 

 be calculated by determining the quantity of radium in a 

 given weight of thorium of known age. I have assumed 

 the monazite to contain on the average 03 per cent, of 

 uranhjm and about 5 per cent, of thorium oxide. From 

 this it follows that i gram of thorium nitrate in equil- 

 ibrium W'ith radium contains about 2-io-^ gram of radium 

 bromide. From the values I have found with samples of 

 thorium of different age, the period of decay for radium 

 lies between 2000 and 3000 years. Alterations in the pro- 

 portions of uranium and thorium would naturally cause 

 corresponding deviations in the value of the constant. 

 The values given, therefore, only indicate approximately 

 the order of magnitude of the period of decay, since I 

 nni ignorant of the exact composition of the monazite used 

 ■i< a source of the nitrates investigated. 



I hope to publish more accurate details shortly in 

 another place. Otto Hahn. 



Chemical Institute, Berlin. 



The Victoria Jubilee Technical Institute, Bombay. 



I SEE in Nati'RE of November 7 advertisements for a 

 principal and professor of chemistry for the \''ictoria 

 Technical College in Bombay. Though I have no con- 

 nection with the institute, and may be charged with un- 

 warrantable interference, I think that it is only fair to 

 intending competitors that certain facts should be made 

 known. 



I wish to point out, in the first place, that the manage- 

 ment of this institution is in the hands of a board of 

 trusteps. and that the principal is not a member of this 

 board, nor has he the right of communicating with the 

 board except through the medium of the honorary secre- 

 tary. The title of principal does not even secure to the 

 holder of it the exclusive right of calling meetings of the 

 itaff, and, in fact, confers nothing more than the power 



XO. 1985, VOL. 77] 



to enforce discipline. On the occasion of the opening of 

 the new laboratories in February last, I was much 

 impressed by the fact that not only was the principal not 

 among the speakers, but that he and his staff were barely 

 referred to, and that their names only appeared in the 

 descriptive pamphlet which was published for the occasion 

 inside the cover and at the end. 



Such were the conditions under which my friend Dr. 

 Mackenzie held the appointment, and it was with no 

 astonishment that I heard on my return from India that 

 he had sent in his resignation. I may add that though 

 Rs. 1000 per mensem with a residence appears to be a 

 good salary, it must be remembered that tliere is no 

 security of tenure of the appointment, and that the resi- 

 dence offered to Dr. Mackenzie lay between the dustiest 

 road and the busiest railway in the heart of Bombay. 



Should any chemist contemplate applying for the 

 " chair " of chemistry with the view of carrying out re- 

 search in his spare time and ultimately improving his 

 position, I should like to remind him that he will do 

 well to take his library with him. There are no scientific 

 books in Bombay. 



Before leaving Bombay I made it clear to some of my 

 friends who are interested in the institute that, in the 

 event of Dr. Mackenzie's resignation being accepted, I 

 should make the facts public, and should warn other scien- 

 tific men against accepting the appointment upon similar 

 terms. Morris W. Travers. 



London, Xovember 9. 



November Meteors. 



Though the general conditions under which the Leonid 

 meteor shower of 1907 takes place are not the most favour- 

 able, still a display of moderate intensity may be expected. 

 The shower promises to be most conspicuous on the night 

 of November 16, when moonlight will interfere consider- 

 ably with observations, especially in the case of the smaller 

 meteors. The following are the times of the various 

 maxima as computed by the writer, the results of these 

 calculations bei ig expressed in Greenwich mean time : — 



Leonid epoch, November 15, gh. The shower, which is 

 of the third order of magnitude, succeeds the epoch, the 

 principal maxima occurring on November 16, I7h., 

 I7h. 30m., and iSh. 30m. There is also a weak secondary 

 epoch on November 17, loh., the shower in this case 

 preceding the epoch, and having its principal maxima on 

 November 16, I3h. 40m., iSh., and November 17, 2h. 



The intensity of the maxima of a meteoric epoch is 

 inversely as the order of magnitude of the shower con- 

 nected with it. Two showers, though of different intensi- 

 ties, will, as may be seen, take place on the night of 

 November 16. 



Scattered through the rest of the month are several 

 interesting minor showers, details of the most remarkable 

 of which will now be given : — ■ 



Epoch, November 22, 4h. Shower of tenth order of 

 magnitude. The shower precedes the epoch, the principal 

 maxima occurring on November 20, 8h., November 21, 

 I4h., and November 22, 3h. 



Epoch, November 25, i2h. This shower, which is of 

 the ninth order of magnitude, has its principal maxima 

 after the epoch as follows: — November 26, ih. 50m., 

 November 27, 2h. 30m. and 6h. Of these, the latter two 

 are the heaviest maxima. 



Epoch, November 29, iSh. The shower, which is of 

 the fifteenth order of magnitude, follows the epoch, the 

 principal maxima occurring on November 29, 23h., 

 November 30, i8h., and December i, 4h. 



Closely associated with the last shower is another, which 

 occurs early in December, is of the fifth order of magni- 

 tude, and has its maxima on December 2, iih., and 

 December 3, 8h. John R. Henry. 



An Optical Illusion. 



The optical illusion described by Mr. Douglas Carnegie 

 in Nature of October iS, 1906, may be explained as 

 follows : — 



The thaumatrope generally reverses its apparent direction 

 of rotation when the observer shuts one eye, or, better 

 still, both eyes alternately, according to the physiological 



