70 Notices respecting New Boohs. 



Last year I examined air vortex-rings produced in the 

 well-known manner described by Prof. Tait*, in the light of a 

 powerful intermittent induction-coil Leyden-jar discharge. 

 The motion is, however, of too continuous a nature to exhibit 

 the advantages of this mode of illumination ; and though the 

 crispations of vibrating rings are well shown, there is no 

 obvious peculiarity noticeable which does not show itself 

 equally well in a steady illumination. 



This paper is only to be regarded as a preliminary note, 

 and, as Prof. Carey Foster has kindly reminded me, the uni- 

 form field as I have drawn it is not quite correct. This indeed 

 will account for the discrepancy between theory and expe- 

 riment mentioned above. 



The appearance of jets of water illuminated intermittently 

 is, as is well known, very striking; and I have long imagined 

 that a waterfall illuminated in this way would be a striking 

 spectacle. The spark is scarcely bright enough for large-scale 

 illumination, though there is nothing to beat it for instanta- 

 neousness. A revolving slit-disk would, however, prove a more 

 manageable and less noisy method, and by a judicious arrange- 

 ment of special lenses it can be made to give plenty of light. 

 But the speed of the disk must be high, and its slits narrow, 

 or the drops will be blurred and their characteristic statical 

 beauty lost. 



X. Notices respecting New Books. 



Geschichte der Elektrizitat. Von Dr. Edm. Hoppe. 

 Leipzig : J. A. Barth (pp. 620). 

 npHE work before us may be characterized as encyclopaedic. It 

 -="- is one of those valuable contributions to scientific literature 

 of which we owe so many to the laborious research of our German 

 friends, but which, for some reason, are found in English, for the 

 most part, only in the form of translations. But Dr. Hoppe's 

 book is not only a valuable collection and resume of all that has 

 been done in Electricity from the earliest times down to the pre- 

 sent date, but it is also a veritable romance, in which the story of 

 discovery in this particular science is told in a most fascinating 

 manner. We are nowadays so familiar with the achievements 

 of science, and so accustomed to see the giant of Electricity tamed 

 and made to serve the purposes of every-day life, that we are 

 apt to overlook the difficulties with which the earlier investigators 

 had to contend ; and it is just here that the charm of such a 

 history as the one before us lies, — that, being familiar with the 

 results of which the original discoverers were in search, we are 

 able to survey their labours, to trace where, having hit upon the 

 right track, they have pursued the truth, till their labours have 

 been crowned with success, and to admire the skill with which 

 they have overcome the difficulties in their way. 

 * 6 Recent Advances, p. 292. 



