April 7, 1882.] 



•* KNOWLEDGE ♦ 



493 



another series of articles, of the fiiiulaineutal jniiu'iplps of 

 electric generators. 



The incandescent light is, beyond doubt, the light of the 

 future, and we ha\c no hesitation in saying that before 

 long we believe it will be proved as much cheaper as it is 

 brighter, purer, and healthier than gas. At the same 

 time we must not lose sight of the fact that it ensures 

 perfect immunity from all those possible catastrophes in- 

 herent to gas. An incandescent lamp, even when broken, 

 is perfectly harmless, and it has been declared that it could 

 be broken in the centre of a barrel of gunpowder without 

 the slightest danger. The reason of this is that the moment 

 the glass is broken, or even cracked, air rushes in to occupy 

 the previously vacuous globe, and coming in contact with 

 the carbon filament, oxidation instantaneously takes place, 

 the filament being thus a continuous conductor no longer. 

 The only danger is when the covering of the wires gets 



4 



damaged, or in any other way allows the current to pass 

 from one wire to the other without going through the 

 lamps ; then great heat would be developed, sufficient, 

 perhaps, to set tire to the building. This danger, however, 

 is easily guarded against by inserting a piece of easily 

 fusible metal, such as lead, in the circuit, which, on getting 

 hot, melts and breaks the circuit, the only inconvenience 

 being the extinction of all the lights in that section, until 

 the piece of lead is replaced. And what is this incon- 

 venience compared to what would result from a gas ex- 

 plosion 1 



Anent the various systems novvf before the public, there 

 is not much to choose between them, but for brilliancy 

 and durability the 8wan certainly leads the way. Thi' 

 Electrolier in the Furniture Court is simply beautiful, and 

 contrasts in the delicate outline of its design with the 

 gorgeous display of Mr. Edison. Nor must we forget 

 Messrs. Elkingtons' show-room, which is very tastily 

 adorned by the Swan light. The Maxim and Lane-Fox 

 systems are both very good, and try hard to outdo each 

 other in their application to delicate glass-work. 



ExpLosivB Pa!nt. — It is stated that the Admiralty have directed 

 that the whole of the xerotine siccative in store at tlie various dock- 

 yards should be immediately destroyed. 



THE GREAT PYRAMID. 



By t}ie Editor. 

 '■pHIS week my remarks upon the Pyramid must be brief, 

 JL for the present number (on account of the approach 

 of Easter week) appears under certain disadvantages. 1 

 take the opportunity of noting sundry objections to my 

 views, which have been suggested by certain readers. 



In the tirst place, many seem quite unaware of the 

 difficulty of orienting a building like the Great Pyramid 

 with the degree of accuracy with which that building 

 actually has been oriented. Oni' gravely asks whetlier 

 (as Narrien long since suggested) a plumb-line, so hung 

 as to be brought into line with the Pole Star, would 

 not have served as well as the great descending passage. 

 Observe how all the real difficulties of the problem are 

 overlooked in this ingenious solution. We want to get a 

 long line — a line at least 200 yards long — in a north and 

 south position. We must fix its two ends, and as the pole- 

 star is not available as a point along the line, we set our 

 plumb-line at the northern end of the line, and our observ- 

 ing tube or hole, or whatever it may be (only it is not a 

 telescope, for we are Egyptians of the time of Cheops, 

 and have none), at the other. The pole-star being at an 

 altitude of 26,V degrees, the plumb-line should be nearly 

 100 yards long,"to be seen (near the top), coincident with 

 the pole-star, from a station 200 yards away. That is a 

 tolerably long plumb-line. Then its upper part (thus to be 

 seen td'thout telescopic aid at night) would be about 260 

 yards away. The observer's eyesight would have to be 

 tolerably keen. 



I am also asked whether a dishful of water would not 

 serve quite as well as a great mass of water, at the corner 

 where the descending and ascending passages meet, to give 

 the reflected rays from a star. It would, and so would a 

 thimbleful — just as a thread of cotton would serve as well 

 as a half-inch rope for the plumb-line just considered. But 

 just in proportion as the water surface was diminished 

 would the difficulty of seeing a star by reflected rays be 

 increased. The builders had, doubtless, good reason for 

 making the descending passage about 4 ft. wide and as 

 many high. It at any rate enabled them to see the pole- 

 star readily, just as the wide field of view of a comet- 

 finder enables the astronomer to bring a celestial object 

 very easily into view. Whatever rea.sou they had for thus 

 securing a tolerably large field of view, they would have 

 precisely the same reason for retaining it undiminished 

 when they used the reflected instead of the direct rays, in 

 observing a star. Now for this purpose nothing short ol 

 the whole lireadth of the descending and ascending passages, 

 would suffice— in other words, no dishful or thimbleful of 

 water would have served their purpose. 



Then the Saturday Review asks why the descending 

 passage should be repeated in the other pyramids when the 

 orientation had already been secured in the Great Pyramid 

 — manifestly quite ignorant of the fact that it would lie far 

 more difficult to take the orientation for one pyramid from 

 another, than to do it independently. It also asks whether 

 the slant descending passages were not obviously meant for' 

 the sliding-down of the King's sarcophagus. Sliding the 

 sarcophagus down that it might afterwards be hauled up 

 the ascending passage ! or if not, what was the ascending 

 passage for ^ and why was it of the same cross section as 

 the descending passage! If the sarcophagus alone had 

 been in question, we may be certain that the pyramid 

 engineers would never have arranged for sliding it 

 down from the level of the entrance to the descending 

 passage, to the place where the ascending passage 

 begins, in order afterwards to raise it by the ascending 



