January 27, 1870. ] 



JOUBNAL OF HORTICULTURE AND COTTAGE GABDENEE. 



65 



paeado-bulbs and leaves resemble Trichopilia suavis, bat in- 

 stead of being dark, heavy green in colour, and leathery in 

 texture, as in that plant, they are light or yellowish green, and 

 the leaf somewhat thin. The spike is drooping, and the 

 flowers, although not large, are very handsome, being yellowish 

 white in the sepals and petals. The lip is faint violet, with a 

 double crescent- shaped line of brown near the base, where it 

 is tinged with yellow. It is a native of Costa Bica, and suc- 

 ceeds best if treated to a little more heat than recommended 

 for the other species. — Experto Crede . 



This 



THE ATMOMETRO-HYGROMETER. 



instrument is designed to give, in a simple, accurate, 



and practical form, the information desirable as to the tempera 

 ture and moisture of the atmosphere, and also the rate of evapor- 

 ation from any moist surface. It consists of a combination of 

 two instruments — 1, The wet and dry bulb thermometers, or 

 what is known as Mason's hygrometer ; and 2, another instru- 

 ment (not so well known), called an atmometer, invented by the 

 late Professor Leslie, of Edinburgh. 



The following is the construction of the new instrument :— A 

 pair of sensitive thermometers, having thin cylindrical bulbs, 

 are fixed on a stand, in an inverted position, as shown in the 

 woodcut; this position of the thermometer bulbs gives more 

 perfect isolation from the temperature of the resting-place and 

 surrounding bodies affecting their indications ; they are fixed 

 sufficiently apart so as not to affect each other. One of Leslie's 

 thin pcrous clay bulbs is fitted to the frame, so as to cover and 

 enclose the bulb of one of the thermometers. In the centre of 

 the stand, between the thermometers, a small glass-tube reser- 

 voir for water is fixed ; a thread of cotton wick reaching to the 

 bottom of this tube is conveyed to and rests upon the porous 

 bulb, which is thus kept continuously supplied with moisture 

 by capillary attraction. The bulb of the thermometer thus en- 

 closed is cooled by the evaporation of water from the surface of 

 the porous clay bulb, in the same way and to the same extent as 

 if it were covered with wet muslin in the ordinary way, and 

 gives, by inspection, all the indications of the wet-bulb ther- 

 mometer ; these, with the indications of the dry-bulb one, form 

 together Mason's hygrometer. From the indications of this in- 

 strument, as is well known, and by the use of Glaisher's " Hy- 

 grometrical Tables," the dew point 

 and state of the air as to moisture 

 are easily obtained and determined. 

 The glass-tube reservoir in the 

 centre of the stand is furnished 

 with a graduated scale. Each 

 degree of water in the tube is equal 

 to one-thousandth part of an inch 

 of depth of water on the evaporat- 

 ing surface or area of the porous 

 ball. These degrees are accurately 

 determined, upon the plan recom- 

 mended by Leslie, for atmometrical 

 degrees. The scale of degrees reads 

 from (0) zero, at the top, downwards 

 — .01, .02, .03, and so on ; ten of 

 these atmometrical degrees, marked 

 .01, are equal to one-hundredth 

 part of an inch of depth of water 

 on the evaporating surface or area 

 of the porous ball ; twenty of these 

 atmometrical degrees marked .02, 

 are equal to one-fiftieth of an inch 

 of depth of water on the area of the 

 evaporating surface ; one hundred 

 of these atmometrical degrees, 

 marked .10, are equal to one-tenth 

 of an inch of depth of water on the 

 surface, and so on. By successive ob- 

 servations of the levef of the water in the reservoir with the 

 scale on it, the rate of evaporation is shown. Should these ob- 

 servations be made and noted daily, then the daily atmometrical 

 degrees added together give weekly, monthly, and yearly, the 

 depth of water evaporated, or the amount of the drainage by the 

 atmosphere from wet or humid surfaces. 



The evaporation of water goes on in nature unceasingly from 

 every moist surface with varying rapidity, according to the dry- 

 ness and temperature of the air. Leslie, however, proved "that 

 it is always proportioned to the extent of the humid surface ;" 

 and also, "that as much water evaporates when the exhaling 



area of the evaporating 



surface appears almost dry, as when it glistens with abundant 

 moisture." If the area, then, of a wet or humid surface and the 

 atmometrical degrees be known, the quantity of water evaporated 

 in a given time is easily calculated. Rule — Multiply the num- 

 ber of square inches of the surface by the atmometrical degrees, 

 and the result is the answer in cubic inches of water, which are 

 easily resolved into measure or weight. Example. — -Suppose 

 the atmometer has indicated .05 in a day, required the quantity 

 of water evaporated from a pond or marsh of the area of an acre - 

 Answer — 1131 gallons, or 5 tons. As a rule, it will be near 

 enough for almost any purpose to reckon the rate of 1 ton per 

 acre for every 10° (.01) of the atmometer. 



Wind has a great effect in increasing the amount of evapor- 

 ation. Leslie found from the indications of an atmometer kept 

 in a still place, compared with one exposed, that they became a 

 measure of the rate of the wind. From these things it is evident 

 that atmometrical observations are as interesting and instructive 

 as those of the rain gauge; indeed, the rainfall of any district is 

 uninstructive unless the amount of evaporation be at the same 

 time determined and given. 



To set the instrument in operation the cap of the reservoir is 

 removed by the bayonet-joint, the tube filled to (0) zero on its 

 scale ; and the thread of cotton wick and also the porous bulb 

 are wetted. Care must be taken not to dirty or grease the porous 

 bulb. 



[The foregoing was sent to us by Mr. Shearer, of Yester 

 Gardens, with the accompanying note : — "This instrument, I 

 think, is that which your correspondent, ' T. H. D.,' requires. 

 I have had it in use here for two years, and consider it of great 

 importance. It is just as necessary as the thermometer, if not 

 more so. I am well aware that experience will soon make 

 anyone acquainted with the proper temperature required in a 

 house for the full development of any plant without looking what 

 the degree of heat is on the thermometer, and also how far the 

 air is charged with moisture by the feeling it produces on the 

 observer ; but we have nothing to guide us what the temperature 

 or the bygrometric state of the atmosphere has been during our 

 absence, except a registering thermometer, and we have now the 

 means with this atmometro-hygrometer, telling us at all times 

 the quantity of moisture which has been evaporated either by 

 night or by" day, and, of course, the temperature at the time it is 

 examined, on the same instrument. Every gardener should 

 have one of these instruments standing out in the garden as well, 

 to tell him when he may sow seeds, or plant out tender plants, 

 or when he should water out-door plants. It would soon point 

 out how absurd the system is of watering plants in all kinds of 

 days, or nearly at all hours, as is sometimes practised. What a loss 

 of beat must take place when a plant is watered on a day during 

 which rapid evaporation has been going on, and which this in- 

 strument indicates at once. In the summer of 1868 our instru- 

 ment here, out in the open field, showed us that in one day 

 nearly 40 tons of water had been evaporated from an acre. Had 

 that acre been covered with a wet cloth I cannot say how much 

 would have been evaporated from the soil in the time— perhaps 

 not much less, or even more had the soil been stirred during 

 the time, as is often done both in gardening and fanning. 



" It was these facts which made Mr. Stevenson construct the 

 instrument referred to. He had previously adapted it to an in- 

 strument which he constructed for the Marquis of Tweedale, my 

 employer, which registers every ten minutes the temperature of 

 the wet and dry bulb, the barometer, and the rain that falls. It 

 is driven by clockwork, stands in the centre of a field, and has 

 been going for two years. The markings are small dots on thin 

 paper, and the thin paper is laid on thick paper with lines show- 

 ing the temperature, &c, and the hours. It is the first of the 

 kind that has ever been erected. There is a somewhat similar 

 instrument at Kew, but the markings are photographed, and it 

 requires a room and gas, while this does in the optn field."] 



PROTECTION versus NON-PROTECTION. 

 In many cases protection encourages all kinds of depredators, 

 and but for severe weather we should often be better without 

 it. For instance, I have fine banks and beds of Endive and 

 Lettuce not at all injured as yet by frost, but some under old 

 sashes and mats when it is very cold, are more or less injured, 

 the crisp hearts being eaten out by rats and mice. All such 

 protection seems to whet the curiosity of depredators, and they 

 seem to fancy that that muBt be better and more valuable to 

 them on which they see extra care bestowed ; thus I have not 

 yet noticed a Strawberry plant grown in the open air, or even 



