Feb. 17, 1888.] 



SCIENTIFIC NE\VS. 



147 



during the month of August at the rate of 40 feet per day. 

 If this is correct it beats the record of European glacier 

 pace by enormous odds, and it pours down 140 million 

 cubic feet of ice daily. It keeps up a supply of icebergs 

 which are continually breaking away from it, some having 

 a cubic capacity of 40 millions of cubic feet. But these 

 dimensions are only those of a shrunken monster. Ac- 

 cording to Mr. Wright it has been fading away rapidly 

 for a long time. He tells us that it has receded several 

 miles up the inlet during the present centurj', and fallen 

 1,000 or 1,500 feet. 



The article on " The Use of Forests " on page 89 of 

 this magazine opens a very interesting and important 

 subject. The deserts of Asia Minor and Africa owe their 

 barrenness more to the destruction of forests by the 

 improvidence of man, and by his wilful devastation as 

 conqueror in barbaric warfare, than to any natural 

 necessity. 



AIR FILTER. 



IN all systems of ventilation the fresh air is drawn 

 from the outside of the building to be ventilated, 

 but in large towns, or in manufacturing districts in the 

 country, the air is more or less charged with soot and 

 dirt. It is therefore, very desirable to filter the air 

 before it reaches the interior of the building, and when 

 mechanical means of ventilation are adopted it is com- 

 paratively easy to make the air pass through suitable 

 filtering media. There are many appliances for effect- 

 ing this, and among them is the one invented by Dr. 

 Moller, of Germany, and made by Messrs. Kiirting Bros. 

 In this apparatus the air is filtered through folds of cotton 

 cloth of suitable thickness, with a rough surface. The air 

 follows the directions indicated by the arrows in the 

 accompanying figs, i and 2, and in order that it may be 

 filtered with as little resistance as possible, there are 



Among the uses of forests is one that I rarely see 

 mentioned, although it is of considerable importance. I 

 refer to their action as flood moderators. Townspeople 

 are not familiar with forests in winter time. 



There are no picnics then, and consequently the fact 

 that a wood which is a pleasant resting-place in summer 

 commonly becomes a wretched swamp in winter, 

 is imperfectly understood. When struggling through 

 such places in January, I have wondered how 

 Robin Hood and his merry men maintained their mirth 

 all " under the greenwood tree." 



This holding of so much water by the decaying leaves 

 and undergrowth is, nevertheless, a great blessing, 

 especially in hilly countries, where otherwise — as in 

 Spain, for example — the rivers are furious torrents in 

 winter and dry in summer. Every wood becomes a 

 reservoir, from which the accumulated waters of the 

 wet season gradually and steadily percolate, supplying 

 the rivers and lower grounds just when water is a bless- 

 ing, and checking the floods when it may become a curse. 



several chambers or filters, E, E, each provided with 

 cloth. There is thus a large filtering area, and we 

 understand that as the air passes only once through the 

 cloth the usual difference of pressure between the 

 incoming non-filtered air and the outgoing filtered air is 

 equal to a column of water only two-tenths of a millimetre 

 high. When necessary the resistance can be reduced to 

 one-tenth of a millimetre, by increasing the filtering 

 surface. As the velocity of the air current is usually 

 small, the particles of dust do not penetrate the cloth, 

 but remain on the surface or fall backwards into the 

 iron chamber or pocket. The cloth should be occasionally 

 taken out and cleaned, and the filter should be fixed so 

 as te be easy of access. 



New Source of Mannite.^J. Kachler {Dingier' s 

 Journal) has obtained mannite by allowing the cambial 

 juice of the pine to stand for some time and ferment 

 slightly. 



