45, COBNHILL, E.G., AND 122, REGENT STREET, W., LONDON. 91 



a means of measuring evaporation from ice or snow. An adjustment for 

 temperature is necessary. Price, 220 



Ditto, large size with Copper Tank 3 10 



128. Glaisher's Thermometer Stand (fig. 91). The Thermometer 

 Stand consists of a horizontal board as as a base, of a vertical board projecting 

 upwards from one edge of the horizontal board, and of two parallel inclined 

 boards, separated from each other by blocks of three inches in thickness con- 

 nected at the top with the vertical board, and at the bottom with the horizontal 

 board, and the air passes freely about and between all these boards ; on the top of 

 the inclined boards is a small projecting roof to prevent, as much as possible, the 

 rain or snow falling on the bulbs of the instruments which are mounted on 

 the front of the vertical board. The bulbs of the Thermometers, &c., all project 

 below the edge of the vertical board, in order, that the air may pass freely over 

 them from all directions. The whole frame is constructed to revolve on an 

 upright post firmly fixed to the ground, as .shown in the engraving; and in 

 use, the inclined side should always be turned towards the sun. 



Price, . . . 330 



129. Stevenson's Thermometer Screen, shown in fig. 90. The louvres 

 in this arrangement are double, sloping in opposite directions, so that whilst 

 there is free access of air to the interior, the radiant heat and rain are excluded. 

 This form of Screen is now found to be the best of any yet invented, for 

 climates similar to the British Islands ; but is not suitable for climates subject 

 to great extremes, such as India or Canada. 



This Screen should stand on open ground and be strongly supported, not 

 under the shadow of trees or houses, and at least twenty feet from any wall, and 

 the floor of the screen to be about four feet above the ground. The door of the 

 Screen should face due north. Price . . . 330 



130. Negretti and Zambra's Set of Standard Instruments on a Screen. 

 Includes N. and Z's. Patent Standard Maximum Registering Thermometer, 

 Standard Minimum Registering Thermometer, and Standard Wet and Dry 

 Bulb Hygrometer, Mounted on Mahogany Board. fig. 88. 550 



Kew Certificates for above ... 10 



The best position for placing the Thermometer Board or Screen is facing 

 the North, at about five feet from the ground, supported firmly to prevent 

 vibration from wind and away from all walls or trees, or if this board be 

 supported by a wall it should be well blocked out from it at least 8 or 12 inchea 

 to allow a free current of air to circulate behind it. 



