OF THE GREAT PYRAMID. 687 



the result of examination has been the crowning of the Pyramid system with some 

 most unexpected features of practical success, and purposed intention. 



To "-correct for temperature," is a very interesting occupation in Natural 

 Philosophy, whether accomplished by calculation, or by instrumental appliances 

 of compensation ; but in practice, and where extreme accuracy is required, it is 

 found that heat is so excessively subtile an influence, and has so many various 

 actions on bodies, sometimes with a secular, and at others with a periodical effect, 

 — that the safest plan by far is, to reduce the amounts of temperature variations 

 themselves to the lowest possible ebb ; and then only have to deal with the effects 

 of the very small residual quantities of heaf so left. Hence at Pulkova, Paris, 

 Edinburgh, and some of the most accurate Observatories in the world, great 

 advantage has recently been found, by placing the sidereal clock of each establish- 

 ment, though armed with a reputed temperature compensation-pendulum, under 

 circumstances where variations could not happen so easily, quickly, or to so great 

 an amount, as in the open room : and every increased degree of such protection 

 has been attended by better performance of the clock. 



The simple placing of the clock in a large closet, has been of sensible service ; 

 but much more good has been obtained by establishing it in a cellar, as at Pul- 

 kova ; and more still, in a cave 95 feet under the surface of the ground, as at Paris. 

 But at no Observatory in the world have they a room, like that of the King's Cham- 

 ber containing the porphyry coffer or weight and capacity standard, in the Great 

 Pyramid, protected by nearly 180 feet in depth, of solid stone on every side. In 

 such a room, the semi-annual variations of atmospheric temperature may be cut 

 down from 50° Pahr. to something less than -01 of a degree. 



Hence the interior Pyramid temperature, must, so far as depends on external 

 natural causes (for of course it is not proof against numerous Arabs inside, with 

 blazing torches), be practically constant from day to night, and summer to winter, 

 and year after year. There is evidently, then, a peculiar temperature to the 

 Pyramid ; which, in Metrology would form a valuable constant. 



What then, is, that temperature ? Or, rather, what used it to be, when the 

 building was in its normal state, throwing off the sun's hot rays from its polished 

 white casing-stones, and having the dryness of its atmosphere corrected by watery 

 vapour effused from its lower, open water- well ? see Plate XXIV. 



As the Pyramid has never been observed by moderns under these circum- 

 stances, we must seek our data from various older quarters ; confined however 

 practically to the French alone ; amongst whom M. Jomakd states that he and his 

 compatriots, in 1799, noted the temperature of the King's Chamber to be 22° 

 cent. ; of the lower part of the dry- well, 25° cent. ; and of certain tombs outside 

 the Pyramid, also, 25°. 



Now these two last sites are nearly on the same level, and a few feet under the 

 general surface of the ground ; it is therefore right that they should have the 



VOL. XXIII. PART III. 8 Y 



