70 ANNUAL OF SCIENTIFIC DISCOVERY. 



upon a bar of gun-metal. The bar is about thirty- eight inches long, and 

 one inch square ; it is supported in a horizontal position upon eight brass 

 rollers, which are carried by levers so arranged that the pressures upon the 

 eight rollers are necessarily equal. The lever frame, with the bar resting 

 upon it, is placed in a box of mahogany wood. The bar is prevented 

 from moving endways by weak brass springs attached inside to the ends of 

 the box, and is prevented from moving upwards by wedges of paper placed 

 under three inverted stirrups. Near to each end of the bar, a cylindrical 

 hole is sunk from the upper surface of the bar to the depth of half an 

 inch, and at the bottom of each cylindrical hole is inserted a gold pin, 

 upon which are cut three fine lines in the direction transversal to the bar, 

 and two fine lines parallel to the axis of the bar. The limiting points of 

 the yard measure are those points of the middle transversal lines which 

 are midway between the longitudinal lines. On the upper surface of the 

 bar the following inscription is engraved : 



Copper. .......... 16 02. 



Tin ........... 21-2 



Zinc ........... 1 



Mr. Baily's metal. 

 Standard yard at at 62.10, Farenheit, cast in 1845. Troughton & Sirnms, London. 



It is necessary to observe that, although the bar was cast so long ago as 

 1845, the standard yai\d has been completed only very lately. 



The standard pound weight is made of platinum, representing, when 

 weighed in vacuo against the last standard Troy pound, 6,999.9,975 grains, 

 of which the last standard contained 5,760 grains. The form of the weight 

 is a cylinder, with a groove surrounding it a little above the middle of its 

 height for the insertion of the fork which is used in lifting it. On the 

 upper end of the cylinder is engraved the following inscription : 



No. 2. 



P. C.t 1844. 

 1 Ib. 



The box containing the weight is mahogany, and when its portions are 

 screwed together the weight is fixed immovably. This mahogany box is 

 placed in a second mahogany box, the lid of which bears the inscription : 



Standard Pound, 1853. 



ON THE CONSUMPTION OF SMOKE. 



The following is an abstract of a paper read before the Society of Civil 

 Engineers, on the consumption and prevention of smoke, by Mr. C. "Wye 

 Williams. 



The object of this communication was, to endeavor to remove the mys- 

 tery which had hitherto obscured, what was asserted to be one of the 

 simplest and best understood processes of nature namely, the combustion 

 of the gaseous products of coal. The nature of flame and smoke was 

 examined, showing that the intense heat caxised by the combustion of the 

 hydrogen, was the direct cause by which the temperature of the carbon 

 was raised to that of white heat, Avhich produced the luminosity of flame. 



