22 



THE GARDENER'S ASSISTANT. 



considerable increase in the strength of the wind. 

 In other words, 



" First rise after very low 

 Indicates a stronger blow". 



During the winter months the rise of the baro- 

 meter almost invariably shows the approach of 

 colder weather, 1 whereas a fall is nearly always 

 followed by milder temperatures than those 

 which have recently prevailed. 



Thermometers. — In order to obtain the tempera- 

 ture of the air, only two of these will be neces- 

 sary — a maximum thermometer to show the 

 greatest heat during the daytime, and a mini- 

 mum thermometer to show the greatest cold at 

 night. The maximum thermometer selected 

 should be what is known as a " Negretti & 

 Zambra" maximum, while the minimum ther- 

 mometer should be a "Rutherford" minimum. 

 Sufficiently accurate and trustworthy instru- 

 ments of both kinds can be obtained for about 

 ten shillings each. The divisions should be 

 marked on the glass tube itself, as well as on 

 the porcelain scale on which the thermometer is 

 mounted. 



Some form of shelter from sun and rain must 

 be provided for these thermometers or their 

 indications will often be unreliable, A simple 

 and effectual screen may be made as follows. 

 First select an open position on a lawn on which 

 to place it. For it must not be under trees, nor 

 within 20 feet of any wall. The screen should 

 be supported by two posts, as shown in the 

 accompanying illustrations (fig. 3). After hav- 

 ing been driven firmly into the ground these 

 posts should each stand 5 feet above the lawn. 

 To the upper part of these posts fasten by screws 

 a half -inch board 1 ft, 10 ins. wide by 1 ft. 

 deep, which, when in position, must face due 

 north. At right angles to this board, at each 

 end, there should be two side pieces of the same 

 thickness and 9 inches wide, to protect the 

 thermometers from the morning and afternoon 

 sun. Then, in order to prevent their readings 

 being affected by the heating up of the back- 

 board at mid-day, let another half-inch board 

 be fixed an inch in front of the other one, so as 

 to secure a space for air between the two boards. 

 The second board should be screwed at the ends 

 to the two side pieces. Let a sloping roof be 

 provided to keep off the rain, and this simple 

 form of screen is very nearly complete. All 

 that remains is to drill three holes an inch in 



i In some districts severe frost occurs with barometer at 29-50 

 to 29 SO, and if the barometer rises there to over 30 ins. but little 

 frost is experienced— ED. 



diameter near the top of the second board and 

 just under the roof, to ensure the ventilation of 

 this part of the screen, and a similar hole in 

 each of the side projections, where indicated in 

 the section (see fig. 3), to ventilate the air-space 



. . . 



' 



Plan 



H 



n 



n 



rr 



Front View Section 



Fig. 3.— Thermometer Screen. 



between the two boards. The thermometers 

 should not be suspended from the second or 

 north board itself, but from two vertical strips 

 of wood an inch wide and half an inch thick 

 fastened to it. The strips should be in the 

 centre of the board, and a sufficient distance 

 apart to suit the holes in the brass plates 

 attached to the backs of the thermometers. 

 When finished, the whole of the screen should 

 be painted with three coats of white paint. 

 Any carpenter could make this screen with the 

 aid of the accompanying illustrations and fore- 

 going instructions. The total cost should not 

 exceed 205. Both thermometers must be sus- 

 pended horizontally by means of brass screws, 

 and the maximum thermometer 2 inches above 

 the minimum. 



In reading the maximum thermometer (fig. 4), 

 the exact position of the end of the mercury 

 should be noted and entered in the observation 



