258 



KNOWLEDGE. 



[November, 1903. 



us. It has long been the dream of philosophers that matter is 

 composed of some primordial substance, arranged in more or 

 less stable configurations, which we terra atoms ; but to the 

 chemist the atom must be absolutely indivisible, or where will 

 the fundamental chemical definitions be ? Meanwhile, the 

 general public looks on with that kind of interest which may 

 be defined as a lively sense of surprises to come. And truly the 

 surprises come, not as single spies, but in battalions ; so quickly, 

 indeed, that a rifiuiiu' of our knowledge, as it was last April, 

 has already taken oc an air of commonplace antiquity. Never- 

 theless, Mr. Hammer's pamphlet on radio-active substances is a 

 welcome contribution to the literature of the subject. In the 

 first place, it traces the "birth and growth and signs'' of the 

 new ideas which are leavening our knowledge ; and this is a 

 worthy task, for at ]iresent the fame of the Curies, well 

 deserved as it is, bids fair to blot out all recollection of the 

 patient toilers who took the first few stejis in the new direction. 

 In the second place, it simply bristles with accounts of experi- 

 ments and facts of importance, and at present we require a 

 good deal of e.\'perimental ballast to give us a feeling of 

 stabilitv. Lastly, ^Ir. Hammer directs attention to some lines 

 of experimental enquiry which are like to be forgotten in the 

 enthusiasm for radio-activity. The first ten pages of Mr. 

 Hammer's pamphlet are devoted to the consideration of 

 fluorescence and phosphorescence. Most of us have seen the 

 glow-worm, and those who have travelled in warmer climates 

 have been charmed by the scintillations of the firefly ; yet how 

 many reflect that in these animals Nature has solved the 

 problem of the economical production of light, which up to the 

 present baffles human intelligence '? What would be the result 

 if we, like the firefly, could produce light without heat, and 

 therefore at about one four-hundredth of its present cost '? 

 Leaving this interesting enquiry unanswered, as it must remain 

 till our knowledge is considerably increased, Mr. Hammer 

 devotes the next thirty-two pages to radio-activity properly so 

 called. Starting with the early experiments of Henry, 

 Niewenglowski, and Becquerel, the development of our know- 

 ledge is traced up to the point at which Prof. Curie found that 

 radium produces heat without any apparent chemical change. 

 As to the physical explanation of this phenomenon, the author 

 has nothing to say : indeed, it was not till after the date at 

 which he wrote that the researches of Rutherford and Soddy, 

 Sir William Ramsay, and Sir William and Lady Huggins gave 

 us a clue. At present it appears that radium atoms sponta- 

 neously decompose, and produce, amongst other products, the gas 

 helium. To this idea Prof. Armstrong objects that in the 

 whole range of chemical knowledge there is no evidence of 

 atomic disintegration occurring under earthly physical con- 

 ditions. But what are we to think ? Helium certainly appears 

 where there was no previous trace of its existence, and that in 

 a manner altogether incompatible with our accepted ideas of 

 chemical action. In addition, Prof. Dewar finds that radium 

 produces heat freely at the temperature of liquid air, and more 

 freely slill at the lower temperature of liquid hydrogen ; at such 

 low temperatures there is, in the whole range of our chemical 

 knowledge, no instance of ordinary chemical action. We are, 

 therefore, certainly bound on an excursion into the unknown, 

 and must shape our theories according to our new lights. It is 

 surprising, however, that no one, in an attempt to explain the 

 unknown by the incomprehensible, has so far dragged the 

 " fourth dimension" into tlje discussion of these results. 



Mr. Hammer next devotes about twenty pages to the pro- 

 perties of selenium, and describes many interesting arrange- 

 ments by which sound may be transmitted " on the wings of 

 light." The action of light on selenium is scarcely less interest- 

 ing than the radio-activity of radium, and its mode of action is 

 at present scarcely less obscure. Perhaps the two will ultimately 

 be found to be related phenomena. 



Mr. Hammer concludes with a short description of the effects 

 of ultra-violet light on various forms of disease. Here, at 

 least, we are tempted to repeat the platitude that there is 

 nothing new under the sun ; for a physician of the time of Queen 

 Flizabeth stated that red light was beneficial to patients suffer- 

 ing from small-pox, while sunlight was distinctly harmful. 

 This result has been found, by Prof. I'insen, to be due to the 

 action of ultra-violet light on diseased tissue ; while it is in the 

 last degree harmful to smallpox patients, it can be utilized 

 with remarkable success in the cure of lupus and similar 



diseases. Whether radium emanations may be ultimately used 

 with success in the treatment of consumption and cancer is 

 not yet known ; but where so much has already been done we 

 at least have grounds for hope. 



"HiSTORV or Philosophy." By William Turner, s.t.d. 

 iGinu & Company.) 12s. 6d.— As a text-book for the student 

 of philosojihy this volume should prove of real service, but the 

 reader must be on his guard as to the obvious bias of the author. 

 Com])iled from the best authorities, this attempt to set forth 

 the succession of schools and systems of philosojihy may be 

 commended for its informing order and admirable method. 

 Comprehensive in its scope, it is clearly and lucidly written, 

 while throughout the work the statements of doctrine are 

 accompanied by valuable bibliographical references. And, 

 finally, the book is furnished with an adequate index. 



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BABY BATS. 



By K. Ltdekker, 



Ever since the days of Pliny it lias been a matter of 

 common knowledge that female bats are in the habit of 

 carryincj their helpless young about with them during 

 their aerial flights for some time after birth. With the 

 exception of one peculiar species, to which allusion is 

 made in the sequel, the young bat always clings to the 

 under surface of its mother's body, wliere it obtains a 

 secure hold among the dense coat of hair. The precise 



