MECHANICS AND USEFUL ARTS. 09 



When, therefore, there was a possibility of its being exposed to damp, thcy 

 based an obelisk, or other granite monument, on limestone substructions; 

 and these last are found to the present day perfectly preserved, while the 

 granite above them gives signs of decay in proportion to its contact with the 

 earth subsequently accumulated about it. I am speaking of Upper Egypt, 

 visited only four or five times in a year by a shower of rain; for in tho 

 Delta granite remains have been affected in a far greater degree than in the 

 Thebaid. Nitre abounds there, and it is remarkable that the obelisks at 

 Alexandria have suffered least on the sides next the sea. 



The Egyptians seldom used granite as a building-stone, except for a small 

 sanctuary in some sandstone temple; and in the later times of the Ptolemies 

 one or two temples were built entirely of granite. But in the pure Egyptian 

 period, that stone was chiefly confined to the external and internal casing of 

 Avails, to obelisks, doorways, monolithic shrines, sarcophagi, statues, small 

 columns, and monuments of limited size, and was sometimes employed for 

 roofing a chamber in a tomb. 



The durability of granite varies according to its qualities. The felspar is 

 the first of its component parts which decomposes, and its greater or less 

 aptitude for decay depends on the nature of the base of which the felspar 

 consists. Egypt produces a great variety of granite, and the primitive 

 ranges in the desert east of the Nile, about thirty-five miles from the Red 

 Sea, supplied the Romans wfth numerous hitherto unknown kinds, as well 

 as with porphyry, which they quarried so extensively in that district; but 

 the granite of the ancient Egyptians came from the quarries of Syene, in the 

 valley of the Nile, and from these they obtained what was used for their 

 monuments. It is from this locality that the name of " Syenite" has been 

 applied to a certain kind of granite; it is, however, far from being all of 

 the same nature, and a small portion of the stone found there is really what 

 we now call " Syenite." 



Already, at the early period of the third and fourth dynasties, between 

 twelve and thirteen centuries before the Christian era, the Egyptians exten- 

 sively employed granite for various purposes. They had learnt to cut it with 

 such skill that the joints of the blocks were fitted with the utmost precision. 

 Deep grooves were formed in the hard stone with evident facility; and it must 

 have been known to them for a long period before the erection of the oldest 

 monuments that remain, the pyramids of Memphis, where granite was 

 introduced in a manner which could only result from long experience. 

 Again, in the time of the first Osirtasen, about 20-50 B. C., granite obelisks 

 were erected at Heliopolis and in the Fyodm, and other granite monuments 

 were raised in the same reign at Thebes, from which we find, that even 

 then the Egyptians had learnt how the damp earth acted on granite when 

 buried beneath it; and this interesting question subsequently suggests itself: 

 How long before that time must the stone have been used to enable them 

 to obtain from experience that important hint which led them to place 

 granite on limestone substructions ? 



WHAT SHOULD MECHANICAL WORKMEN BE TAUGHT? 



The following extracts from an address on the above subject, recently 

 delivered at the South Kensington Museum, London, by J. Scott Russelk, 

 F. R. S., contain some views on the education of mechanical workmen which 

 are both novel and interesting. 



