554 



SCIENTIFIC NE^VS. 



[June 15, iS 



days tnat old Indians tell us are as oppressively hot as 

 those of Calcutta, some say even more so. The cause 

 of this is similar to that described above. Although the 

 sun does not rise so high at midday, it is higher 

 in the morning and evening over London at summer 

 time than over Calcutta. Usually we are screened by 

 our less transparent atmosphere, but there are days 

 when even our British sky is as clear as that of the 

 tropics. 



The dominating cause of the bitterness of arctic 

 climate is the long arctic night — the months of darkness 

 during which the earth is continually radiating into 

 space the heat it has received from the sun. The effect 

 of only a few hours of such radiation is shown by com- 

 paring the temperature of the earth's surface at 3 p.m. 

 with that of 3 a.m. in our own summer time. 



Thus when the time arrives for the departure of the 

 sun from the arctic and antarctic regions, they cool 

 down continuously, are only prevented from reaching 

 the temperature of space by the atmospheric clothing 

 which checks this radiation to some degree, but in a less 

 degree than it checks the radiation here and nearer the 

 equator. This diminished efficiency of the atmospheric 

 jacket is another important factor co-operating with the 

 long continuance of the outflow of heat. 



The reason why the atmosphere does less for the pro- 

 tection of these parts of the earth is that it contains far 

 less aqueous vapour than in those regions where the 

 night is not long enough for the condensation to become 

 as nearly complete. But this aqueous protection is not 

 altogether lost. The dry land of the polar regions 

 receives it in another form of protecting jacket — that of 

 snow, and hence it is quite possible that certain regions 

 may exist close to the poles, even at and around the 

 poles themselves, where the ground may be barely 

 frozen during the winter, in consequence of receiving a 

 deep coat of snow immediately the long night begins, 

 and when this is melted by the returning sun, a rich 

 vegetation may spring forth and flourish luxuriantly, as 

 it actually does in those parts of Siberia where the 

 winter temperature of the air is lower than in any other 

 known region of the world. 



At such places, i.e., on inland arctic plains, the greatest 

 possible variations of cHmate occur. There the con- 

 tinuous summer rays go on heating and heating the soil, 

 with little variation, during every twenty-four hours, 

 with no variation at all at the actual poles, and the con- 

 tinuous winter radiation through the less resisting air 

 brings the winter temperature at the snow surface 

 nearly to that of outer space, or the lowest possible. 



But there are arctic regions where the summer is cold. 

 It is so at Smith's Sound, for example, just where our 

 arctic explorers have done most of their work. These 

 are glacier regions, where the ice from the mountains is 

 pouring down into the sea to form a freezing mixture 

 with the oceanic salt. This summer climate is quite 

 different from normal inland arctic summer. 



— »^3«^>i^«f-<- — 



The Atmosphere on the SuMjirr of Ben Nevis. — 

 Although the air at this station is most frequently satu- 

 rated with moisture, there occurs at irregular intervals 

 dryness exceeding anything hitherto recognised in the 

 Sahara, in the deserts of Central Asia, and in the north 

 of Mexico. Such exceptional dryness, was observed in 

 1886 from I a.m., March nth, until the night between 

 the 1 2th and the 13th. 



FURNACE FOR LOW-CLASS FUEL. 



PROBABLY few of our readers have any conception 

 of the enormous quantities of small coal which is. 

 treated as waste at the pits. We refer to that which ia 

 too small for domestic use, or for the firing of steam 

 boilers, etc. Some of it is sold for blacksmiths' forges, 

 but a very large proportion is treated as not, worth the 

 cost of carriage. This is due, not to any unreasoning 

 prejudice, but to the real difficulty of burning it on 

 ordinary grates without a considerable loss. When the 

 coal is very small, and is mixed with a good deal of dust,, 

 much of it falls through the grate bars ; and if this be 

 prevented by placing the bars close enough together 

 there is an insufficient supply of air to the fuel, unless 

 there is a very strong chimney draught. A strong 

 draught of air, however, means a considerable loss of 

 heat carried away by convection up the chimney. 



In some cases the difficulty has been overcome to a 

 certain extent by mixing a little tar with the coal dust, 

 and then pressing it into the shape of bricks. This 

 usually goes by the name of " patent fuel," and is chiefly 

 used for marine boilers, and for railway locomotives in 

 France and other continental countries. It is not much 

 used in this country, as the expense of making the bricks 

 renders this fuel as dear as good coal of large size. 



With these facts before him, M. Michel Ferret, of 

 Paris, has for a long time endeavoured to construct a 

 furnace in which low-class fuels of all kinds and coal or 

 coke dust could be burnt. We know that he has 

 achieved a considerable measure of success, and think, 

 therefore, that many of our readers will be interested in 

 having some particulars of his invention. The furnace 

 he first introduced is shown in section in Figs, i and 2, 

 and this he exhibited at the Smoke Abatement Exhibition 

 held at South Kensington. The leading feature of the 

 furnace is that there are several shelves or floors, on 

 which layers of fuel a few inches thick are placed, and 

 the air, admitted at the bottom, gradually travels over 

 the surface of the fuel on all the shelves until the whole 

 of the oxygen is taken up. After the furnace has been 

 started with a little fire on each shelf fresh fuel is put on 

 the top shelf, and from this it is raked on to the shelf 

 immediately below, and from the second shelf on to the 

 third, and so on successively. In this way a large 

 surface of hot fuel is exposed to the oxidising influence 

 of heated air, and by the time the residue is raked on to- 

 the grate at the bottom complete combustion of the 

 carbon has taken place, and there is nothing left but 

 clinker and ash. The chimney draught required is very 

 slight, because the air does not have to pass through the 

 fuel, as in an ordinary furnace, and it is easy to regulate 

 this to a great nicety, and this is another source of 

 economy. 



More recently M. Ferret has introduced the furnace 

 shown in Figs. 3 and 4, in which he uses a series of 

 narrow shelves, prismatic in section, instead of the wider 

 shelves shown in Figs, i and 2. The whole furnace is 

 charged with fuel, and the narrow shelves are so arranged 

 that as the fuel burns away below its place is taken by 

 fuel falling down from the top, and in this way he avoids 

 the labour of raking the fuel from one shelf to another, 

 as in Figs, i and 2. It is probable that in the new 

 arrangement there is some slight loss of fuel, owing to 

 the formation of carbonic oxide caused by the reduction 

 of some of the carbonic acid formed in the lower strata 

 of the fire. On the other hand, the furnace can be charged 

 and left for twenty-four, and it is said even forty-eight 



