FOR GENERAL READERS. 



FRIDAY, JULY 27th, 1888. 



CONTENTS. 



Scientific Table Talk 



The Naturalist at the Sea-Side : 



III. Shore Collecting 



The Bridge across the Arthur Kill {Mm.) 

 Poisons in the Workshop — II.... 

 Whirlwinds and Waterspouts — l.(illus.) 



The Stability of the Fauna 



General Notes ... 



Standards of Light and Illumination 

 (illus.) 



Natural History : 



Stauronotus Maroccanus (illus.') ... 



Sensitiveness of Plants 



Fauna of Water-Mains 



PAGE 



■• 73 



74 



75 

 76 



77 

 7* 

 79 



Locusts in Europe ... 

 Miscellaneous Notes 



PAGE 



.. 84 



Fruits 85 



Reviews : 



Whence Comes Man ; from " Na- 

 ture " or from " God " ? 86 



Proceedings of the Institution of 

 Engineers and Shipbuilders in 

 Scotland 87 



Journal of the Society of Telegraph 

 Engineers and Electricians ... 87 



Abstracts of Papers, Lectures, etc. : 



Northern Institute of Literary and 

 Scientific Societies 88 



PAGE 

 South London Microscopical and 



Natural History Club ... 88 



Artificial Formation of Rocks ... 89 



The Healing of Fishes 91 



A Big Thing in Guns 92 



Correspondence : 



Meteorites and Lightning — Habits 

 of the Hessian Fly — A Circle 

 Problem— The Cosmical Origin 



of Hailstones— The Lantern Fly 94 



Recent Inventions 95 



Announcements... ... ... ... 96 



Sales and Exchanges- 9*> 



Selected Books 9 6 



Meteorological Returns 96 



SCIENTIFIC TABLE TALK. 



By W. Mattieu Williams, F.R.A.S., F.C.S. 

 The mysterious behaviour of the satellites of Jupiter 

 during transit (i.e. when travelling between us and 

 the planet, and consequently appearing to cross his 

 disc) has been observed and studied during the last 200 

 years. The phenomena in question are most decidedly 

 displayed by the fourth satellite, which performs as fol- 

 lows : — On approaching the planet it becomes rapidly 

 and increasingly fainter, until it touches the edge of the 

 visible disc (the " limb," as it is technically called). 

 When actually seen upon the limb it shines with mode- 

 rated brilliancy for about ten or fifteen minutes; then it 

 suddenly disappears, and remains invisible, in spite of 

 using more powerful telescopes ; after about ten or 

 fifteen minutes more it reappears, but no longer as a 

 bright moon. It has now become a dark spot, faintly 

 grey at first, but gradually growing darker and darker, 

 until it equals the blackness of its own shadow on the 

 planet. 



As a matter of course these curious changes have sug- 

 gested many speculations, mostly unsatisfactory, until 

 Mr. Edmund J. Spitta took up the subject, and by in- 

 vestigating it experimentally has at last solved the 

 mystery. 



His first series of experiments were conducted by 

 cutting out a disc of cardboard, 3| inches diameter, to 

 represent the planet, and other little discs of paper to 

 represent the satellites, the proportions of their dimen- 

 sions corresponding to those of the objects they repre- 

 sented. In the course of the experiments they were 

 tinted with various shades, from white to dark grey, 

 illuminated strongly by means of a condensing magic- 

 lantern. These were placed about sixty yards distant 

 from a telescope, and the results ol placing the mock 

 satellites in front of the mock planet were carefully 

 observed. 



The " albedo " or intrinsic reflected brightness of each 

 of the differently shaded moons, and also that of the 



planet disc, were determined by means of Pritchard's 

 wedge photometer, and it was found that when a moon of 

 equal albedo to that of the planet was held by its fine 

 wire stalk in front of the planet it became invisible, with 

 smaller albedo than the planet it appeared dark, with 

 greater it formed a bright spot, the differences varying 

 with the gradations of tint. This is simply what any- 

 body would expect a priori, but it was clearly desirable 

 to establish it positively under the conditions of the 

 experiment. 



The next series of experiments were made to determine 

 the effect of proximity of the planet to the satellite with- 

 out actual superposition. These proved that as the 

 larger and brighter disc approached the smaller and less 

 brilliant the latter appeared less and less bright, the 

 phenomena of the approach of the satellites to their 

 primary being closely imitated. 



Still, the mysterious changes, the extinction of the 

 bright moon, and its reappearance as a dark spot remained 

 unexplained, but so far the imitation of planet and moons 

 was imperfect ; the mock Jupiter was a flat disc, not a 

 sphere. 



Another series of experiments followed those above 

 described ; in these the disc of cardboard was replaced 

 by a sphere of plaster of Paris 3| ins. diameter, the other 

 conditions of these experiments being similar to the 

 preceding. 



The result is thus described by Mr. Spitta : — "It was 

 found that the moons with the same albedo appeared 

 black and grey as before, but what was far more surpris- 

 ing, that all the phenomena of the dark transit could be com- 

 pletely reproduced. I have witnessed the real phenomena 

 very repeatedly, but I did not contemplate a reproduc- 

 tion from the employment of such simple means." He 

 proceeds to describe this as follows : — " Whilst the dark 

 moon having an albedo of 0-13 wa? advancing towards 

 the artificial planet its light becan o fainter and fainter, 

 but still of sufficient brilliancy to remain a bright spot 

 when on the limb. Still continuing its journey across 

 the artificial planet, and having arrived at an angle of 



