76 



SCIENTIFIC NE^A/^S. 



[Jan. 27, 18 



moisture is increased or diminished, but tliat the capacity 

 of air to absorb moisture is increased when the tempera- 

 ture is raised. Our judgment is, in fact, independent of 

 the actual quantity of moisture present, and in summer 

 or winter we talk of the air being either dry or wet, not 

 because there is any difference in the quantity of mois- 

 ture present, but because in summer the capacity of the 

 air to absorb moisture is greater, whereas in winter the 

 atmosphere is nearly saturated. According to Mr. Leslie, 

 its capacity for moisture is about doubled for every in- 

 crease of twenty-seven degrees Fahrenheit. For this 

 reason when air is overheated, without being brought 

 sufficiently in contact with water, it too rapidly absorbs 

 moisture from our skin and lungs, and this withdrawal 

 of moisture has a cooling effect. Moreover, according 

 to Dr. Urc, the blood-vessels on the surface are then 

 contracted, while other parts of the bodj', not being ex- 

 posed to such an influence, are surcharged with the 

 fluids repelled from the extremities. Then, again, there 

 is the fact that the decomposition of animal and vegetable 

 matters given off from the lungs and skin is more 

 readily effected when the air is hot. It will thus be 

 seen that there are many and good reasons why the air 

 of the rooms we live in should not be rendered too hot 

 or too dry, and that it is essential to accompany any 

 system of heating with efficient means of ventilation, to 

 insure a good supply of fresh air and sufficient moisture 

 to give a feeling of comfort to those present. 



Formerly churches and large buildings were often 

 heated by means of pipes conveying either hot air or the 

 hot products of combustion from a fire, but in nearly all 

 cases in this country such a system has been abandoned, 

 partly for the reasons above stated, partly because of the 

 difficulty of obtaining a uniform temperature, and partly 

 because of the risk from fire owing to the overheating 

 of pipes. A circulation of hot water is now generally 

 used instead, as with this the temperature of the pipes 

 can never exceed 200'' F., and it can be reduced below 

 this exactly as required. 



There remains, howe^^er, the class of stoves in which 

 the air of the room is heated by allowing it to pass 

 through chambers provided in the stoves. In this 

 system the objections to close stoves are to a great 

 extent removed, and may be entirely overcome if care 

 be taken not to over-heat the stove, and to provide a pan 

 of water on the top of the stove to prevent excessive 

 dryness of the air. Typical examples of these stoves 

 are given in the accompanying illustrations,* and it 

 will be seen that if the air to be heated is taken 

 from the outside of the building, these stoves may be 

 made to materially assist healthy ventilation. Fig. i 

 represents a slow combustion stove fed with fuel from 

 the top, and with an external casing enclosing an air 

 space. There are also air cells in the middle of the 

 stove, and inlets for air at the bottom and outlets at 

 the top, all the air spaces being indicated by arrows. In 

 this stove the air of a room can be made to enter at the 

 bottom and discharged at the top, and the same air can 

 be heated over and over again. But a still better way 

 is to connect the bottom of the stove with a fresh air 

 supply taken from the outside of the building, as shown 

 in Fig. I, so that a continuous current of fresh warm air 

 may be delivered into the room. This stove is much 



* We are indebted to Messrs. Musgrave and Co. for Fig. i ; to 

 Messrs. J. F. Farwig and Co. for Figs. 2 and 3 ; and to Messrs. 

 Doulton and Co. for Fig. 4. 



used for hospitals, for the halls of houses, and for 

 churches and school-rooms. In Figs. 2 and 3 we have- 

 the vertical and transverse sections of another stove 

 similar in principle; and the makers very properly 

 point out that it is most desirable to let the air inlet at 

 the bottom be in direct communication with the external 

 air. Such a stove need only be charged with small coke 

 once in ten or twelve hours. Fig. 4 is another example 

 of a close stove with means of heating air passing 

 through it, and here we gee that the air supply is drawn 

 from a passage through the floor of the room. In this 

 case the internal and external parts of the stove are- 

 made of fire-clay tiles, iron being used only for bracing 

 the various parts together and for the doors. With 

 this construction it is more easy to maintain a uniform 

 temperature, as the fire-clay, being a refractory material 

 and a bad conductor of heat, does not cool quickly, even 

 if the fire is neglected and gets low ; nor is it easy to 

 overheat it. As, therefore, the fire-clay does not get too 

 hot, and as it is a bad conductor of heat, the air passing 

 through and over it does not get excessively dry, if 

 suitable arrangements are made. On the other hand, 

 the very fact that fire-clay is not so good a heat conductor 

 as iron, renders the latter more economical to use,, 

 although less easy to regulate. A good example of the 

 fire-clay stove has been fitted up in the Smoking Room 

 of the Hotel Metropole, and in this case four stoves are,., 

 so to speak, made into one. In other words, the stove has 

 four fires — one on each side. 



Gum Trees. — The rapid growth. and the value as timber 

 and fuel of many of the Australian gum trees (eucalyptus), 

 have induced planters in this country to attempt their 

 cultivation ; but the experiments have proved beyond 

 question that none of the species is sufficiently hardy to 

 bear the winters of the eastern and central parts of this 

 kingdom. In some localities they escape injurious eifects 

 dui-ing a cycle of comparatively mild winters, giving rise 

 to hopes that they are permanently established ; but a 

 colder winter, or a cold, wet autumn, followed by an 

 ordinary winter, kills, or irremediably injures the young 

 trees. Of the many species tried at Kew, for instance, 

 only one. Eucalyptus Gunnii, has lived through many 

 years without some kind of protection, and the 

 young shoots of this have often been destroyed. A 

 tree of Eucalyptus Gunnii, which for many years 

 bore the incorrect name of Eucalyptus polyanthema, stood, 

 some thirty j'ears ago, near the old Mesembryanthemum 

 house, near or on the site of the present Orchid house, 

 and many will remember it as the first Australian tree 

 they had seen growing in the open air in England. It 

 was then perhaps about 20 ft. high, and, so far as we 

 remember, it was not materially injured by the intense 

 frost of 1860-61, when large specimens ot Cupressus 

 macrocarpa and Pinus insignis were killed outright. That 

 season the thermometer fell, on two or three occasions, 

 below Zero at Kew, where, if we remember rightly, it 

 has never since been so low. Some years later, when 

 the new range of houses was built, the alterations 

 necessitated the removal of this tree, and it was transferred 

 to the western slope of the mound on which the Temple of 

 iEolus stands, near to No. 2 Museum, and the result was 

 that it died to the ground, or nearly so ; but, what was 

 surprising, it threw up new stems,,and is still flourishing. 

 — Gardeners' Chronicle. 



