Aug. 



1884.] 



♦ KNOW^LEDGE ♦ 



161 



the moon, 'till you assure me that the people in the moon 

 are as little acquainted with their advantages as we are 

 with ours, and that they take our earth for a planet, with- 

 out knowing theirs is one too." 



" Do not doubt it," said I, " we appear to them to per- 

 form very regularly our function of a planet. 'Tis true, 

 they do not see us make a circle round them, but that is 

 no great matter. That half of the moon which was turn'd 

 towards us at the beginning of the world, hath been 

 turn'd towards us ever since ; and those spots in her, 

 which we have thought to look like a face, with eyes, nose, 

 and mouth, are still the same ; and if the other opposite 

 half should appear to us, we should no doubt fancy another 

 figure from the different spots that are in it : not but that 

 the moon turns upon herself, and in the same time that she 

 turns round the earth, that is, in a month ; but while she 

 is making that turn upon herself, and that she would hide 

 a cheek, for example, and appear somewhat else to us, she 

 makes a like part of her circle round the earth, and still 

 presents to us the same cheek : so that the moon, who in 

 respect of the sun and stars, turns round herself, in respect 

 of us, does not turn at all : they seem to her to rise and 

 set in space of [about] fifteen days ; but for our earth, it 

 appears to her to be held up in the same place of the 

 heavens. 'Tis true, this apparent immobility is not very 

 agreeable for a body which should pass for a planet, but it 

 is not altogether perfect ; the moon has a kind of trembling, 

 which causes a little edge of her face to be sometimes hid 

 from us, and a little edge of the opposite half appear ; but 

 then, upon my word, she attributes that trembling to us, 

 and fancies that we have in the heavens the motion of a 

 pendulum, which vibrates to and fro."* 



(To be coniiHued.) 



THE INTERNATIONAL HEALTH 

 EXHIBITION. 



XIII.— WATER AND WATER-SUPPLIES— (confinued). 



THE excellent filter-case described in our last communi- 

 cationj not only provides for the outflow of every 

 drop of filtered water, but can be taken to pieces and 

 thoroughly rinsed when desired. A glance at the sectional 

 figure (Fig. 22) will explain how this may be accomplished. 

 To the apparatus thus constructed Messrs. Doiilton ife Co. 

 have adapted the Patent Manganous Carbon Block, which 

 is exempt from the disadvantages of the ordinary " block " 

 principle. The latter are prone to harbour organic and 

 other impurities to such an extent as to render them quite 

 unwholesome. Thus, the Rivers Pollution Commissioners 

 state that "the property which animal charcoal possesses in 

 a high degree, of favouring the growth of the low forms of 

 organic life, is a serious drawback to its use as a filtering 

 medium for potable waters.''^ The Army Medical Report, 

 again, states of charcoal in porous blocks, that, " after a 

 time the purifying power becomes diminished in a marked 

 degree, and water left in contact with the filtering medium 

 is apt to take up impurity again, § 



It is well known that carbon is adapted to filtering pur- 

 poses, on account of its property for appropriating and 

 condensing oxygen, which it parts with to organic sub- 



* Of course the lunar vibrations are not real tremblings, as 

 liere described. They arise, in fact, from the nniformity of her 

 rotational motion, combined with her steady, though not abso- 

 lutely uniform motion, on a path slightly inclined to the plane of 

 her equator. — R. P. 



+ Ut supra, p. 139. J " Sixth Report," p. 220. 



§ " Army Medical Report," XIX., p. 170. 



stances brought to it, and oxidises or burns them up. 

 Animal charcoal is peculiar in its decolourising or bleaching 

 effects, and vegetable charcoal has the power to deodorise. 

 A combination of the two deprived of all adventitious 

 matters is, therefore, of the highest value to filter manu- 

 facturers who seek to purify water for drinking. To 

 entirely discard such a valuable medium would indeed be 

 to "fly in the face of Providence." The problem which 

 here arises may be solved in either of two ways : — (a.) The 

 purified mixture of carbon should be such as to provide for 

 a constant reparation of its properties ; or (p) It ought to 

 be easily replaceable at a very trivial cost. 



We have already stated that experiment has shown the 

 " block " system to be faulty, because it soon becomes over- 

 taxed, and no amount of boiling or scrubbing can restore 

 it to its pristine active condition. The only remedy is to 

 be sought for in a renewal of the block, but the frequent 

 necessity for such an operation has the great disadvantage 

 to be a very expensive process. Such was the state of 

 affairs when the block system " ruled the roast," that the 

 domestic filter came to be looked upon either as a trouble- 

 some luxury, or, when neglected, as a dangerous con- 

 trivance. Yet the necessity of an efiicient household water 

 purifier made itself sorely felt, and Messrs. Doulton i Co., 

 as one of the oldest and most celebrated firms of filter 

 manufacturers, felt themselves called upon to remedy 

 matters. They consulted Dr. Albert J. Bernays, F.C.S., 

 the Professor of Chemistry at St. Thomas's Hospital, and 

 the result of his researches, which extended over a period 

 of three years, is now embodied in their " Patent Man- 

 ganous-Carbon Filter." Fig. 25 shows one of these filters 



Fig. 25. — Doulton's Patent " Manganous-Carbon " Block Syphoia 

 Filter and Case. For the use of tourists and erplorers. 



as adapted to the use of tourists and explorers. The carbon 

 block can be immersed in any pond or stream, and a 

 draught of pure water sucked through the flexible tube. 

 These filters may also be used upon the " Syphon " principle ; 

 the block may be placed in a pail of water, and the flexible 

 tube permitted to hang over its side, below the level of the 

 block ; once set going by suction, their action thereafter 

 becomes continuous. 



The value of manganous-carbon as a filtering medium 

 has been set forth by Messrs. Doulton in their prospectus^ 

 in the following outline of its reactions : — " With the 

 object of rendering the charcoal pure in the manganous- 

 carbon filter, each grain of the medium receives a coating 

 of manganese dioxide, and is then reournt at a high tem- 

 perature in absence of air. By this means the hydrogen- 

 bearing impurities are oxidised and removed. At the 

 same time the manganese dioxide is reduced to a lower 

 oxide. These lower oxides rapidly reabsorb oxygen from 

 the air, becoming again converted into hyclrated dioxide, 

 which, in its turn, yields oxygen to the organic matters 

 present in the water. Thus the manganese acts as a carrier 

 of oxygen from the air to the impurities in the water, 

 oxidising or burning up the latter, and then again becoming 

 revivified by the atmosphere. Manganese also exerts a 

 preventive influence on the growth of organisms, the 



