Oct. l'O, 1882.] 



♦ KNOWLEDGE ♦ 



39 



will, if the E M F remains constant, vary in strength with 

 the resistance in the battery. Thus supposing a battery of 

 ."i crlls in series yielding a current of -1 Ampere to produce 



•i'l'.'l'^ 



I I H^ 



<D- 



Fig. 1. 



a deflection of 5", two such batteries placed side by side as 

 ill Fig. 1, will yield -2 Ampere and produce a deflection of 

 10°. The equation in the second case becomes 



because in adding the second battery we practically double 

 the size of the original cells, and so halve the resistance. 

 The EM F is not affected, as the energy or potential of the 

 current is independent of any variation in the size of the 

 plates. 



Tliis topic will be resumed in our next. 



NIGHTS WITH A THREE-INCH 

 TELESCOPE. 



By a Fellow of the Royal Astronomical Society. 



(Continued from pane 311.) 



IF the reader will lish with a power of 70 or 80 between 

 /5 Cygni and Delphinus, some 7° south-east of the former 

 star, lie will strike upon that very curious object, 27 Messier, 

 Vulpeculse — the so-called " Dumb Bell " nebula, of which 

 ridiculous pictures appear in certain works on popular 

 astronomy. We have done what we could to present a 

 portrait of tliis nebula in Fig. .')6. 



M. Vulpccul; 



H Driiconii 



The sprawling constellation Draco, which straggles over 

 so much of the circumpolar sky, is our next in order for 

 examination. From its situation the amateur can scarcely 

 expect to scrutinise many of its chief objects in suacession 

 without getting a back-ache, and a still' neck to boot, so 

 inconveniently are they placed. Let us, however, express 

 a liope that the intellectual pleasure to be derived from 

 such a search may quite outweigh its concomitant physical 



discomfort. If we draw a line from -/ Draconis, through 

 /3, and carry it on twice the distance between them, Wf 

 shall strike 17 Draconis, a pretty and intirestiiig triple. 

 fi Draconis, a close but easy pair, is shown in Fig. .">7. 

 Rather more than 1 \° south of /5 Draconis is a small but 

 very pretty double star, 147 of Piazzi's hour XVII. It 

 is invisible to the naked eye. If we draw a line from 

 the Pole Star to y Draconis, and fish on it, about half 

 way between those stars, with a low power, we shall light 

 upon that strange object, Herschel .'57, IV., Draconis. 

 This is the nebula which our greatest living English 

 spectroscopist. Dr. Huggins, found to be gaseous, in 18C4. 

 A'iewed in the instrument employed for the purpose of 

 these papers, it presents the appearance of a large pale 

 blue star out of focus. South-east of t Urs;e Minoris 

 to Draconis will be found. It is a wide and ea.sy pair. 

 159 Draconis, half-way between y and i, ajipears in the 

 books as a triple star. It will require an extremely tine 

 night and a high power, however, to show the comes to 

 the principal star, whose light and proximity (juite over- 

 power it ; so that it will ordinarily appear as a very wide 

 double only, in a three-inch telescope, a Draconis is a wide 

 pair, but the colours are very pretty. The last object in 

 this constellation which we shall look at to night, t Dra- 

 conis, will form a severe test, at once for the observer's 

 instrument and his eye, and for the state of the atmo- 

 sphere. He must employ the highest power at his com- 

 mand, and even then the companion will often be involved 

 in the diffraction ring surrounding the larger star. Fig. -^S 

 gives an idea of this star when caught at moments of the 

 best vision. 



D 



EARTHQUAKES IN THE BRITISH 

 ISLES.— I. 



R. MILNE, recently returned from Japan, notes that 

 men in England pay less attention to earth 

 tremblings than they merit, though we have no such reason 

 for noting them as they ha\ e in Japan. We aic, however, 

 all interested in the question whether this, our country, is 

 liable — even at lon^r interv.als of time — to the influence of 

 destructive earthquakes. We know that there arc coun- 

 tries which seem as firm and unshaken as our own is wont 

 to be — countries which have remained for . enturies undis- 

 turbed by any save the faintest indications of earth- 

 tremor, whicli have yet been suddenly visited by those 

 fierce throes which hurl in a few minutes the largest and 

 best built cities to the ground. We ask ourselves whether 

 the inhabitants of Lisbon could have felt less secure than 

 we ourselves do of immunity from serious danger! Yet 

 we know that without warning, that large city was made 

 in a few moments a mere heap of ruins, in and around 

 which lay the unburied bodies of sixty thousand of her 

 inhabitants. 



We often have had evidence that our country is, at lea.st, 

 not wholly unaflected by the action of subterranean distur- 

 bances. An area one hundred and fifty miles long ami 

 some seventy miles wide-- possibly much larger — was dis- 

 turbed only some twelve years ago by a smart shock of 

 earthquake. The eflects produced by the shock were not 

 very remarkable — indeed, when one compares them witli 

 the efl'ects of the late earth-throes in Panama, British 

 earthquakes generally remind us of the old line, 



" Sloiitos pnvturiuiit, imscitur liiliciilus imis." 

 The solid foundations of England may be shaken, with no 

 more remarkable results than the disturbance of a few 

 people in bed at the time, noises " resembling the scurrying; 



