JOURNAL OF HORTICULTUEE AND COTTAGE GAEDENEE. 



[ January 25, 1872. 



doners, we recommend the more general adoption of outside 

 blinds. They are useful for shading in summer as well as for 

 retaining heat in winter, and at this season they may be used 

 even during the day on the roofs of many of our glazed struc- 

 tures without injury to their tenants. The following is an 

 arrangement we would recommend. 



The bUnd is fixed at the top of I he roof, the roller passing 

 up and down when required, as shown in the accompanying 

 drawings. A thick 

 string passes from 

 the hand round a 

 pulley fixed at the 

 corner of the roof, 

 and continues on- 

 ward to the wheel at- 

 tached to one end of 

 the pole. Supposing 

 the wheel to be at 

 the bottom — that is, 

 lot down, the string : 

 will then be turned -^ 



many times round '-'■-^. - --..._--- 



the large wheel, say '^^"^:;i;rv_;^Z_r-— ^^^^-— "^' 



6 inches in diame- "" 



tcr. The action is 



thus : — You pull the string passing over the pulley, which un- 

 winds the string turned many times round the wheel, and as 

 the strmg is gathered into the 

 hand the po'e turns round, winds 

 up the blind, and proceeds with 

 its burden until safely landed 

 under its wooden covering at 

 the top. There is some little 

 accommodation required to learn 

 how best to get the far end of 

 the pole to reach its destination 

 ;.t the same time as the near 

 end ; but this, like all such mat- 

 ters, simply requires a slight 

 observation to make the arrange- 

 ment simple and effectual. Tlie 

 covering or locker for the bUnd, 

 wiieu drawn up, works on hinges 

 and shuts down, resting on the 

 roof, thus secui-ing the blind from rain or damp. 



The bearers should be four in number, about 3 inches from 

 the roof, half an inch thick, to preserve the heat generated 

 within, and to exclude more effectually the outer cold. The 

 bearers to project beyond the glass at the lower ends. Let the 

 blind down 1 foot beyond the glass, which serves the pui'pose of 

 a bhud for the front in keeping out the frost. 



The blind is of a brown coarse stout canvas, such as is 

 used for paclcing, 2 yards wide, at 9d. per yard. Before fixing 

 up stretch it on the ground, and brush well over twice with 

 boiled linseed oil. 



As a proof of the cooling powers of radiation, and as a hint 

 sometimes useful when the ice-house fails, we copy the follow- 

 ing from our contemporary Nattire. 



ICE-MAKING IN THE TROPICS. 



The most marked example of the influence of radiation of 

 heat on temperature is its influence on the jjroduction of arti- 

 ficial ice by the natives of India. 



The fields in which the ice is made are low, flat, and open; 

 and the ice is produced in large quantities when the tem- 

 peratui-e of the air is 16° or 20° F. above the freezing point ; 

 and the plan followed is an interesting example of accurate 

 observation applied to practical purposes by a people now 

 ignorant of sc;e<ice. The same process has been employed 

 from time immemorial in India with scientific accui'acy ; and 

 while the theory was explained by Dr. WeUs (Essay on Dew, 

 1814) , the practical application was not so well imderstood ; 

 and this first led me to investigate the subject in India (Experi- 

 mental Essay; Jour. Asiatic Society, Calcutta, vol. ii., p. 80.) 



The following method is employed by the natives of Bengal 

 for making ice at the town of Hooghly, near Calcutta, in fields 

 freely exposed to the sky, and formed of a black loam soil upon 

 a substratum of sand. 



The natives commence theii' preparations by maiking out a 

 rectangular piece of ground 120 feet long by 20 broad, in an 

 easterly and westerly direction, fi'om which the soil is removed 

 to a depth of 2 feet. This exoavatiou is smoothed, and is 



allowed to remain exposed to the sun to diy, when rice straw 

 in fiiuall sheaves is laid in an oblique direction in the hollow, 

 with loose straw upon the top, to the depth of lA foot, leaving 

 its surface half a foot below that of the ground. Numerous 

 beds of this kind are formed, with narrow pathways between 

 them, in which large earthen water-jars are sunk in the ground 

 for the convenience of having water near, to fill the shallow 

 unglazed earthen vessels in which it is to be frozen. These 

 dishes are 9 inches in diameter at the top, diminishing to 

 4/'o inches at the bottom, Ij-'J, deep, and ,^o of an inch in thick- 

 ness ; and are so porous as to become moist throughout when 

 water is put into them. 



Dui'ingthe day the loose straw in the beds above the sheaves 

 is occasionally turned up, so that the whole may be kept dry, 

 and the water-jars between the beds are filled with soft pure 

 water from the neighbouring pools. Towards evening the 

 shallow earthen dishes are arranged in rows upon the straw, 

 and by means of small earthen pots, tied to the extremities of 

 long bamboo rods, each is filled about a third with water. The 

 quantity, however, varies according to the expectation of ice — 

 wliich is known by the clearness of the sky, and the steadiness 

 with which the wind blows from the N.N.W. When favour- 

 able, about 8ozs. of water is put into each dish, and when less 

 is expected, from 2 to 4 ozs. is the usual quantity ; but in all 

 cases more water is put into the dishes nearest the western 

 end of the beds, as the sun first falls on that part, and the ice 

 is thus more easily removed, from its solution being quicker. 



There are about 4590 plates in each of the beds last made, 

 and if we allow 5 ozs. for each dish, which presents a surface 

 of about 4 inches square, there will be an aggregate of 239 gal- 

 lons, and a surface of 1530 square feet of water in each bed. 



In the cold season, when the temperature of the air at the 

 ice fields is under 50" F., and there are gentle aii-s from the 

 northern and western direction, ice forms in the course of the 

 night in each of the shallow dishes. Persons are stationed to 

 observe when a small film appears upon the water in the dishes, 

 when the contents of several are mixed together, and thrown 

 over the other dishes. This operation increases the congeal- 

 ing process ; as a state of calmness has been discovered by the 

 natives to diminish the quantity of ice produced. When the 

 sky is quite clear, with gentle steady airs from the N.N.W. , 

 which proceed from the hUIs of considerable elevation near 

 Bheerboom, about one hundred miles from Hooghly, the freez- 

 ing commences before or about midnight, and continues to 

 advance until morning, when the thickest ice is formed. I 

 have seen it seven-tenths of an inch in thickness, and in a few 

 very favoui'able nights the whole of the water is frozen, when 

 it is called by the natives soUd ice. When it commences to 

 congeal between two and thi-ee o'clock in the morning, thinner 

 ice is expected, called paper ice ; and when about four or five 

 o'clock in the morning the thinnest is obtained, called flower 

 ice. 



Upwards of 250 persons of all ages are actively employed 

 in seeming the ice for some hours every morning that ice is 

 procured, and this foi-ms one of the most animated scenes wit- 

 nessed in Bengal. In a favourable night upwards of 10 cwt. ef 

 ice will be obtained from one bed, and from twenty beds up- 

 wards of 10 tons. 



When the wind attains a southerly or easterly direction 

 no ice is formed, from its not being sufficiently dry ; not even 

 though the temperature of the air be lower than when it is 

 made with the wind more from a northern or western point. 

 The N.N.W is the most favourable direction of wind for 

 making ice, and this diminishes in power as it approaches the 

 due north or west. In the latter case more latitude is allowed 

 than from the N.N.W. to the north. So great is the influence 

 of the direction of wind on the ice, that when it changes in 

 the course of a night from the N.N.W to a less favourable 

 dii'ection, the change not only prevents the formation of more 

 ice, but dissolves what may have been formed. On such oc- 

 casions fi mist is seen hovermg over the ice beds, from the 

 moisture over them, and the quantity condensed by the cold 

 wind. A mist in like manner forms over deep tanks during 

 favourable nights for making ice. 



Another important cu-cumstance in the production of ice is 

 the irmount of wind. When it approaches a breeze no ice is 

 formed. This is explained by such rapid currents of ah' re- 

 moving the cold air before any accumulation of ice has taken 

 place in the ice beds. It is for these reasons that the thickest 

 ice is expected when during the day a breeze has blown from 

 the N.W., which thoroughly dries the ground. 



The ice dishes present a large moist external surface to the 



