MECHANICS AND USEFUL ARTS. 103 



quantity if required. In the centre aisle, also, the air will be plenti- 

 fully admitted, and by simple machinery the whole of the ventilation 

 can be easily regulated. In order to subdue the intense light in so 

 large a building covered with glass, all the south side of the upright 

 parts, and the whole of the angled roof, are to be covered with can- 

 vas or calico, so fixed as to allow a current of air to pass between the 

 canvas and the roof. Magnifying-glasses, working on swivels, placed 

 at short distances in the galleries and elsewhere, will aid in affording 

 a perfect general view of the Exhibition. 



From other sources we learn that on the north side of the main 

 building is another apartment 936 feet long and 48 feet wide, to con- 

 tain machinery. The height of the building is 66 feet, except in the 

 transept, which is 108 feet high, so as to inclose a group of trees. 

 The main parallelogram is formed into 11 divisions longitudinally, 

 alternately 24 feet and 48 feet wide, with the exception of the great 

 central walk, which is 72 feet wide. 



TEST FOR LUBRICATING COMPOUNDS. 



MR. JAMES NASMYTH has invented a test of the quality of various 

 kinds of oil for lubricating purposes, which, he claims, is superior to 

 any other. It is founded on the assumption, that permanent fluidity 

 is the valuable quality in any lubricating compound, and that many 

 oils, such as linseed, though they at first answer capitally the purpose 

 intended, become thick and viscid after one or two days' use, so ay 

 to be worthless. The test consists simply of a plate of iron, 4 inches 

 wide by 6 feet long, on the upper surface of which are six equal-sized 

 grooves. The plate is placed in an inclining position, say one inch in 

 six feet, and equal quantities of the various kinds of lubricating sub- 

 stances are poured into the grooves. That which retains its fluidity 

 longest will reach the bottom first, though other oils may keep ahead 

 of it for two or three days. London Mining Journal, March 30. 



