262 



• KNOWLEDGE - 



[May 4, 1883. 



After long consideration I have been able to devise small 

 instrnincuts, which I can send throuf;h the post, and from 

 the indications those give I can tell with accuruoy what 

 lenses are required. 1 have suited many cases in this way 

 by correspondence, when the eyes of the correspondents 

 differed greatly in focus. 



Lenses of pebble, rock crystal, or, as it is termed by 

 mineralogists, quartz, keep a clear, bright polished surface 

 very much better than glass, and most persons prefer them. 

 A correspondent of Knowi.edgk inquired recently if these 

 lenses were not cut at varying angles out of the quartz 

 crystals, and whether this would not cause them to perform 

 badly. Jfy experience is that this is a matter of but little 

 consequence where the image formed by the lens is viewed 

 without magnification. 



Still, first-class opticians should keep pebble lenses cut 

 at right angles to the axis of the crystal, though they are 

 necessarily more expensive. 



Such lenses, when tested by polarised light, should give 

 concentric coloured rings. Lenses not cut at right angles 

 to the axis of the crystal give coloured bands. 



You are doubtless aware that a glass eye is frequently 

 worn by a person who has lost an eye either by an acci- 

 dent or by disease. But few people are aware how skilfully 

 these glass eyes are made and fixed. They are kept in 

 their place simply by atmospheric pressure, and can be 

 removed and replaced without pain. They move in 

 unison with the sound eye, and it is at times almost impos- 

 sible to tell the diflTerence between the artificial eye and 

 the real one. 



A celebrated surgeon states that he knew a case where 

 a lady who had a glass-eye got married, and although she 

 had been married two years, the husband had not dis- 

 covered that one of her eyes was artificial. 



I do not think a lady would be deceived in a similar 

 manner. Ladies generally know " How to use their eyes," 

 and I think a lady would find out if a gentleman had a 

 glass-eye before he had been courting her a week. 



And now let me say, in conclusion, that there are many 

 points with regard to my subject at which I have scarcely 

 glanced, and several to which I have only briefly referred. 



My papers have been on what to see and how to see it. 



I am well aware that I have treated most imperfectly 

 these important subjects. I could not possibly have done 

 justice to them in the space at my disposal. A long course 

 of papers might be devoted to them, each more interesting, 

 because more complete, than those I have written. 



The charms of a forest in autumn, the changing hues of 

 the clouds at sunset, the exquisitely modulated tints of a 

 rainbow, the glory of the heavens on a clear night, filled 

 with the innumerable suns which we call stars, all depend 

 on light and colour for their lieauty, and each of these 

 would furnish themes for papers on which I should scarcely 

 dare to try my hand, knowing as I do how much better 

 they could be treated by the Editor of this iournal. 



Electric Lighting at Kimberley, South Africa. — 

 A correspondent, writing to the Ehctrician, says : — " This 

 installation consists of 32 Brush arc lamps, supplied by 

 two 16-light machines driven from a countershaft by a 

 Robey engine of 20 nominal horse j)ower. One circuit, 

 three and a half miles in length, extends round the 

 Kimberley mine, the other circuit, four miles in length, 

 to De Beer's mine, down Du Toit's Pan and Victoria 

 Roads. The wires are carried partly on the roofs of the 

 houses, partly on iron poles, and the light is at present 

 giving great satisfaction. 



A DREAM OF INFINITY. 



By De Quincey, after Ricuter. 



[So many have asked to refer them to some work containing tho 

 quotation with which I closed my first and sixth lectures at St. 

 James's Hall, tliat I have thought it might be well to give the 

 ])assage in these pages, as I am in tho habit of quoting it. I fancy 

 it differs somewhat from the original, to which I liave not referred 

 now for many j-ears. I used to depart purposely from the original, 

 in ])Iiices, for convenience of recitation ; and it seems to mo likely 

 that, writing now in Belfast,* away from my books, I niay not be 

 able to i|Uote tho passage quite correctly. It runs, in Do Quincey, 

 very nearly as follows : — ] 



GOD called up, from dreams, a man into the vestibule 

 of Heaven, saying. Come thou hither, and see the 

 glories of my kingdom. And to the angels that stood 

 around his throne, God said. Take him ; strip from him 

 his robes of flesh ; cleanse his vision, and put a new breath 

 into his nostrils : only, touch not with any change his 

 human heart, the heart that weeps and trembles. It was 

 done ; and with a mighty angel for his guide, the man 

 stood ready for his infinite voyage ; and from the terraces 

 of hea\-en, without sound of farewell, they passed into 

 infinite space. 



Sometimes, with the solemn sweep of angel wings, they 

 passed through Zaharas of darkness, through wildernesses 

 of death, that divided the worlds of life. Sometimes they 

 passed over thresholds quickening under prophetic motions 

 from God. Then, from beyond depths counted only in 

 heaven, light dawned as from a sleeply film. By unutter- 

 able pace, they passed to the light, the light by unutterable 

 pace to them. In a moment, the rush of planets was 

 around them; in a moment, the blaze of suns was upon them. 



Then came eternities of twilight, that revealed, but 

 were not revealed. On the right hand and on the left 

 towered gigantic constellations, that by self repetitions, by 

 answers from afar, by counterpositions, built up triumphal 

 gateways, whose archways and architraves, horizontal, 

 upright, rested, rose, "at altitude, by spans — that seemed 

 ghostly from infinitude. Without number were the arch- 

 ways, beyond memory the gateways, past counting the 

 architraves. Within were stairs that scaled the extremities 

 around. Above was below, below was above, to the man 

 stripped of gravitating body. Depth was swallowed up by 

 height insurmountable, height was swallowed up by depth 

 unfathomable. 



On a sudden — as thus they rode from infinite to infinite ; 

 on a sudden — as thus they tilted over abysmal worlds ; a 

 mighty cry arose that systems more mysterious, worlds 

 more billowy, other heights, other depths, were coming, 

 were nearing, were at hand ! 



Then the man sighed and paused, shuddered and wept ; 

 his overladen heart uttered itself in tears ; and he said : — 

 " Angel, I will go no farther ; for the spirit of man acheth 

 with this infinitude. Insufterable is the glory of God ! 

 Let me lie down and hide me in the grave from the perse- 

 cution of the infinite; for end I see there is none." And 

 from all the listening stars that shone around there issued 

 a choral voice, " Angel, thou knowest that the man speaks 

 truly ; end is there none that ever yet we heard of." " Is 

 there no end 1" the Angel solemnly demanded : " Is there 

 indeed no end 1 and is this the sorrow that kills you 1 " 



But no voice answered, that he might answer himself. 



Then the Angel threw up his glorious hands to the 

 heaven of heavens, saying : — 



" End is there none to the Universe of God ; lo, also 

 there is no bcfirinning." 



• This may serve to ex])laiu the occurrence of certain misprints 

 in last number of KNOwi-EncE, especially in letter 798, which I had 

 no opportunity of correcting. 



