l62 



NATURE 



[February i6, 189; 



time when the student receives it until he has made his 

 last note, every operation ought to be in an order for 

 which very definite reasons can be given, and the com- 

 pleted work ought to be of such a character that any- 

 thing added to it would be superfluous ; anything taken 

 from it would leave it imperfect ; and any change in the 

 order of its various parts would be to its detriment. This 

 character of work is generally sought after in the separa- 

 tion of metals from a solution ; but the rest of a qualita- 

 tive analysis, namely the preliminary examination and the 

 testing for acids, is too often a collection of odd opera- 

 tions, which, if the student is lucky, will lead him sooner or 

 later to the desired result, but if he is unlucky may fail to 

 do so through no fault of his own. 



Chapman Jones. 



POPULAR LECTURES ON PHYSICAL 

 SUBJECTS. 



Gemeinverstdndliche Vortriige aus de/n Gebeite der 

 Physic. Von Prof. Dr. Leonhard Sohncke. (Jena : 

 Gustav Fischer.) 



IT is a matter of common remark that the books on 

 scientific subjects which reach us from Germany are, 

 as a rule, so special and detailed in character as to be 

 totally devoid of interest, except to those immediately 

 concerned with the subjects of which they treat. This 

 being the case, it is all the more refreshing to meet with 

 such a collection of popular addresses as Prof. Solfncke 

 has gathered together in the volume before us. He has 

 not restricted himself in his choice of subjects to any one 

 branch of physics ; on the contrary, the nine lec- 

 tures of which the book is made up represent as 

 many different divisions of natural philosophy, and were 

 delivered quite independently before various audiences 

 in Germany. 



The first lecture of the series bears the somewhat 

 obscure title, " What then ? " and was suggested by a 

 great strike among the coal-miners of Westphalia, which 

 led to a temporary cessation of the German coal supply. 

 The author depicts what would be the consequences if 

 the world's coal supply were exhausted, in terms almost 

 as pathetic as those of Prof. Jevons which moved an Eng- 

 lish Parliament to appoint a commission on the subject. 

 But recognizing that, after all, coal is only stored up solar 

 energy. Prof. Sohncke endeavours to look at the brighter 

 side of the question by discussing the possibility of utilis- 

 ing the sun's energy in other forms, and so enabling man 

 to remain " lord of creation " even in those days when the 

 entire available coal supply of the world reposes on the 

 shelves of some scientific museum. 



Equally spontaneous is the lecture on " Migratory 

 Mountains," in which an account of a holiday visit to the 

 north-east corner of Germany gives an opportunity of de- 

 scribing the formation and movements of the mammoth 

 sand-dunes in that locality. 



Of the other lectures, that entitled " The revolution in 



our views concerning the nature of electrical actions " 



will probably commend itself to most readers because it 



treats of a subject now exciting general interest. It con- 



NO. 1216, VOL. 47] 



tains a short history of the arguments and experiments 

 which led to the substitution of the ether theory of elec- 

 trical action in the place of the older action-at-a-distance 

 theories. While admitting the existence of a medium 

 which transmits both optical and electrical disturbances^ 

 the author thinks it more probable that gravitation is a 

 true action-at-a-distance, and in so doing he tacitly denies 

 that a medium is a necessity. The notion of an empty space 

 is so foreign to English men of science of this generation, 

 that we certainly consider Prof. Sohncke's summing-up 

 of the question to be worthy of attention. He says : — 

 " Even if we could finally succeed in proving that action- 

 at-a-distance is really the result of a transmission through 

 some medium, we must not suppose that all difficulties 

 are then removed. For the process of such a transmis- 

 sion is by no means simple, and cannot be explained 

 without further assumptions ; on the contrary, very for- 

 midable difficulties arise even here. Directly we Xxy to 

 give a concise explanation of the compression of a body 

 and its subsequent expansion when performing elastic 

 vibrations, we find that a choice must be made between 

 two assumptions equally hard to accept. Either matter 

 is itself capable of compression and expansion, or else it 

 consists of separate vibrating atoms to which we must 

 assign the property of exerting mutual forces on each, 

 other at a distance." 



From a purely scientific standpoint, the lecture on 

 " Newer theories of atmospheric electricity and thunder- 

 storms " is undoubtedly the most valuable of the series, 

 the subject being one on which Prof. Sohncke can speak 

 with some authority. After describing the older theories 

 of the origin of electrical charges in the atmosphere, he 

 discusses those newer ones which were suggested by the 

 discovery of Hertz that ultra-violet light facilitates the 

 discharge of electricity from a charged body. Of these 

 the best known is that of Arrhenius, who supposes the air, 

 ordinarily a dielectric, to be rendered feebly-conducting 

 by the action of light. According to this theory, the earth 

 is negatively charged, and when its atmosphere is illumi- 

 nated some of the charge is conducted away to the clouds. 

 The conduction must be electrolytic, otherwise the air 

 would become charged. Prof. Sohncke objects to this 

 theory mainly on the ground that the discharging action 

 of light cannot be considered as due to the air in any 

 way, since it is manifested only when the light vibrations 

 fall on, and are absorbed by, the negative electrode. 

 Further, it is not easy to see how elementary gases such 

 as oxygen and nitrogen can be electrolytes. In con- 

 cluding he defends his own theory, according to which 

 atmospheric electricity is produced when a cloud laden 

 with particles of ice meets another charged with water 

 drops, the electrification being due to the friction of ice 

 against water. In support of his view the author quotes 

 the fact that hailstones are found to be electrified on 

 reaching the ground. 



The appearance of a volume like the present one in- 

 variably gives rise to some regrets that the whole earth 

 is no longer of one language and one speech, but we hope 

 that some friend of popular science may be induced by 

 the contents of the book to furnish a translation for 

 English readers. 



James L. Howard. 



