45, CORNHILL, E.C., AND 122, REGENT STREET, W., LONDON. 09 



No. 139. Negretti and Zambra's Registering Lincl's Anemometer. 

 Several modifications of Lind's Wind Gauge have at various times been in- 

 vented by Sir W. Snow Harris, Mr. Wood and others, with a view to make ifc 

 self-recording, but the only one that proves satisfactory in actual service, is an 

 arrangement manufactured by Negretti and Zambra at the suggestion of Mr. 

 Forbes, of Inverness. The improvement consists of a third tube of the same 

 internal diameter, connected by a bend at the Zero point of the instrument, 

 into which the water overflows and is collected from the leeward tube of the 

 syphon. The water thus collected being the maximum amount of depression 

 produced in the syphon representing the extreme force of the wind. 



Table showing the Force of wind on a square foot, for different 

 heights of the column of Water in Lind's Wind-Gauge. 



Price, 330 

 140. Improved Portable Air Meter, for measuring the velocity of 



currents of Air in Coal Mines and Ventilators, Flues, &c., of Public Buildings, 



Hospital and Prison Wards, &c., &c. (figs. 110 and 111.) 



By means of this Air Meter, the rate at which a current of Air is moving 



can be ascertained in a few minutes. The Instrument shows from one foot to 



ten million feet. 



The long hand marks up to 100 feet ; each division on the large circle represents one 



foot traversed by the current of air. In setting down a reading of the hands, the long hand 



takes the units and tens places. The five other hands follow respectively. 



EXAMPLE. 



Millns. 100 thds. 10 thds. thds. hds. long hand. 



Places the hands take when set down in figures 00|0|0|OjO|00 

 Reading of the above diagrams ... 1 | J 9 | 9 99 



In setting down the position of the hands observe the following rule : No hand can 

 mark a figure unless the foregoing hand has arrived at the " 0." For example, suppose the 

 long hand pointed to 99, the hundreds' hand would appear to point to a figure, but it could 

 not mark the figure until the long hand pointed to the zero. The same rule applies to all 

 the hands. When a hand appears to be between the divisions, write down the lowest figure 

 next the hand. 



The catch on the rim of the instrument will stop or allow the hands to run without 

 affecting the action of the fans. 



