February 24, 19 10] 



NA TURE 



491 



During all these periods the planet was kept under 

 observation at Flagstaff, and during none of them 

 were any such canals recorded. We are, therefore, 

 sure that seasonal change cannot explain them, and 

 that two years ago, and also eleven, thirteen, and 

 fifteen years ago, no such canals existed. In Martian 

 chronology this means that not only did they not e.xist 

 in their present state during the previous Martian 

 year, but also not four, five, and six Martian years 

 before that. It is also fairly sure that they were not 

 in existence thirty and thirty-two years ago, inasmuch 

 as Schiaparelli never saw them. 



Lastly, a further point disclosed by the Flagstaff 

 observations must be reckoned with, a point of very 

 singular significance. It was long ago discovered 

 there that (see Bulletin No. 8 of the Lowell Observa- 

 tory), while the great majority of the canals are 

 quickened into conspicuousness alternately every six 

 Martian months, first from the south and then from 

 the north polar cap, certain ones respond only to one 

 or the other cap, remaining inert to the action of its 

 antipodal fellow. To be sure, therefore, that the new- 

 canals were really new to Mars, the old drawmgs 

 had to be examined on this score too. Here again 

 the records were decisive. No such canals had ever 

 appeared before from the quickening of either cap at 

 the time when, had they existed then, they should 

 have showed. 



The canals in question, therefore, proved to be, not 

 simply new canals to us, but new canals to Mars. In 

 the canal system they are novae in fact or function, 

 and as such are the most important contribution 

 to our knowledge of the planet of recent years. 

 For let us see what they imply. In form they are 

 like all the other canals, narrow, regular lines of even 

 width throughout, running with geometric precision 

 from definite points to another point where an oasis 

 is located. This oasis resembles all the other oases, 

 a small, round, dark spot. They partake, therefore, 

 of all the peculiar features of the canal system, fea- 

 tures which I have elsewhere shown make it im- 

 possible of natural creation, that is, of being the result 

 of any purely physical forces of which we have cogni- 

 sance. On the other hand, the system exactly 

 resembles what life there would evolve under the 

 conditions we know to exist. The present phenomena, 

 then, show that the canals are still in process of 

 creation, that we have actually seen some formed 

 under our very eyes. 



Thus, on every point which had to be considered, 

 the records furnished conclusive evidence that the 

 canals in question could not have existed in past 

 Martian years in the condition in which we observe 

 them to-day. Their previous non-visibility could not 

 have been due to any of the causes which might 

 possibly affect it, to wit: — (i) Want of size; (2) any 

 personal equation of the observer ; (3) improved instru- 

 mental or atmospheric means; (4) distance (all these 

 are negatived by their striking conspicuousness) ; (5) 

 NO. 2104, VOL. 82] 



phase ; (6) regular seasonal change ; and last (7) uni- 

 hemispheric seasonal change. 



It will be perceived that the proof that these canals 

 are novae has been possible, and only possible, through 

 the long systematic work done on the planet here for 

 the last fifteen years. Without such .1 complete system 

 of records _the certainty that the canals in question 

 were new canals io Mars could not have been reached. 

 Percival Lowell. 



Lowell Observatory, Flagstaff, A.T. 



PROPERTIES OF POLONIUM. 



T^HE statements regarding polonium which 

 ■'■ appeared in the report from Paris reprinted from 

 the Times in Nature of February 17, must have 

 surprised inany readers to whom polonium has been 

 a familiar substance for the last ten years. It may be 

 of interest to review briefly our present knowledge of 

 polonium and the bearing of the recent work of Mme. 

 Curie and Debierne upon it. 



Polonium was the first of the active substances 

 separated from pitchblende residues by Mme. Curie. 

 \'arious methods of concentration were devised bv her, 

 with the result that preparations of polonium mixed 

 with bismuth were early obtained many thousand 

 times more active than uranium. Marckwald later 

 separated from 15 tons of pitchblende about 3 milli- 

 grams of intensely active material which he called 

 radio-tellurium, since it was separated initially with 

 tellurium as an impurity. By dipping a copper plate 

 into a solution of this substance, he obtained a deposit 

 of weight not more than i/ioo milligram, which was 

 far more active than an equal weight of radium. It 

 was soon recognised that this preparation was identical 

 with polonium, for it gave off the typical a. radiation, 

 and had the characteristic rate of decay of that 

 substance. L'nfortunately, Marckwald was not aware 

 at the time of separation of the great importance of 

 testing whether lead appeared as a product of trans- 

 formation of polonium. Before such an experiment 

 could' be made, the polonium had to a large extent 

 been transformed. 



Polonium is one of the numerous transition elements 

 produced during the transformation of the uranium- 

 radium series. It is half-transformed in about 140 

 days,, emitting a particles during the process. Ruther- 

 ford showed in 1904 that polonium was in reality a 

 transformation product of radium itself. Radium at 

 first changes into the emanation, and then successively 

 into radium .A, B, C, D, E, F, radium F being 

 identical in all respects with the polonium directly 

 separated from a radio-active mineral. When the 

 radium emanation is allowed to decay in a sealed glass 

 tube, the walls of the tube are coated with an invisible 

 deposit of pure radium D, radium E, and radium F, 

 but the amount of the latter to be obtained in this 

 way is far too small to be weighable. 



The amount of polonium present in any radio- 

 active mineral can easily be calculated. .Since the 

 radium and polonium (radium F) in a mineral are in 

 radio-active equilibrium, the same number of a particles 

 are expelled from each per second. Since polonium 

 is half-transformed in 140 days and radiuin in 2000 

 years, the former breaks up 5000 times faster than 

 the latter. The maximum amount of polonium to be 

 obtained from a mineral is in consequence onlv 1/5000 

 of the amount of radium. In 1000 kilos, of pitchblende 

 containing 50 per cent, of uranium, there are present 

 170 milligrams of radium. The weight of polonium 

 is about 1/5000 of this, or about 1/30 milligram. It 

 is thus obvious that to obtain i/io of a milligram of 

 pure polonium, several tons of high-grade pitchblende 

 must be worked up. The most natural source of 



