202 



KNOWLEDGE 



[Jan. G, 1882. 



tho ohnin C.C tight. PrrhapB we mny finy that if the height from 

 A to B in (im ia vorj' oitninon) 11 in., tho hole ftt C may lio 8J in. 

 from n. ThiB will t;nv a i|inisi-cqiiatorial movement to the 

 tclescopo for Ujnilim unci places not very far north uml smith 

 of tho Bnmo latitmle. Tho nao of this contrivance is very 

 simple. Tho bar BM is placed duo north and snutli 

 (M, of cmirse, towanls tho south). A star is Kot into the 

 field, and tho chain C.C Btretched ti)?ht and made fast. Then the 

 obscn-er will find timi on rotating the telescope horizontally round 

 A, the end O will be so shackled as to constrain it to follow the 

 given object. A few miscellaneous hints may conclude what we 

 have to say im the telesco|x; itself. First, the reader may wish to 

 test it for ils freedom from colour and aberration. For the first, 

 lot him turn tho instrument on to tho round edge (or " limb ") of 

 tho moon, and first move tho eye-picco mthin tho focus by means 

 of the milled hcml F, then a purple fringe should appear on the 

 lunar limb. On moving the eye-piece outside the focus, this should 

 give place to a green ring. A telescope that exhibits this setiucnce 

 of phenomena is achromatic. For spherical aberration, focus the 

 tcIe8CO))c on a tolerably bright star, with the whole aperture, and 

 then put a diaphram of, say, li in. aperture over the object glass. 



Fig. 2. Fig. 3. 



and see if the star remains accnrately in focus. If it does, spheri- 

 cal aberration is cured too. A bright star in focus with a power of 

 150 should present the appearance of Fig. 2, by no means that of 

 Fig. 3, which latter indicates a practically worthless object-glass ; 

 nor should any light haze appear about bright stars or planets. 

 Next week we hope to set the young observer fairly to work. 



THE SO-CALLED TUNNEI^WORM. 



IN La Nature, for December 10, M. Maximo U^lJne remarked 

 that exaggerated ideas are prevalent respecting the defective 

 ventilation of tho great, tunnel of St. Gothard, and in particular that 

 tho supposed development of a special parasite, the tnnnel-worm, 

 must bo regarded as problematic. To this Professor F. A. Forel 

 replies that tho malady is perfectly authentic, and is due to a 

 parasitic worm, the Duodenal Anchylostoma (the stiff-jaws of the 

 first intestine, one might say), which attacks the mucus membrane 

 of tho jejunum and duodenum (the first parts of the small in- 

 testines), and sucks the blood like a leech. He says that Dr. Ed. 

 Bngnion, a professor at Lansanne, has recently published a remark- 

 able investigation, in which he has discussed the question thoroughly. 

 He has examined forty-one well authenticated cases among the 

 workmen in the Gothard tunnel, attacked by chloron and anaemia 

 (ghastly paleness and bloodlessness). The presence of the 

 tunnel-worm was established in these cases either by post-mortem 

 examination or from the recognition of tho eggs in voided matter. 

 As for the origin of the disease, it is not, as has been thought, a 

 new one, or produced by either the high temperature and bad venti- 

 lation of tho tunnels. The worm is very common in Egyjit, where 

 it causes Egyptian chlorosis, and in Italy. Its appearance in the 

 St. Gothard tunnel is easily explained, when wo consider, on the 

 one hand, the habits of tho thousands of workmen employed there 

 (all Italians, crowded in tho villages of Airolo and do Goeshenen), 

 and the migrations of tho intestinal worm. It passes, says M. 

 Bugnion, the first part of its existence in tho mud and slime of 

 watcr-|>ools*, and it ia from drinking dirty water containing young 

 larviu of the parnsito that tho infection is received. Since tho 

 nature of the disease has been known, worm medicines have been 

 oaod, and the doctors of the St. Gothard tunnel have lost no more 

 of the patients attacketl by the ailment, which had been called 

 provisionally the St. Gothonl ana'mia, and which should hereafter 

 be calleil, ProfcBsor Forel thinks, by the pleasing name " Anchylo- 

 atomasia." 



SCIENTIFIC PARADOX. 



TIME was when itinerant lecturers made a great point of what 

 was then called the " hydrostatic paradox," by which the 

 weight of a pint of water might be made to burst asunder the 

 strongest cask — but although that age has passed, yet we ore not 

 without some paradoxes which yet remain in the ordinary treatment 

 of physics. 



That steam at lOO'C. should heat a bath of Calcium ClUoride up to 

 ItS'C, is jiaradoxical at first sight ; but it is an established fact, 

 and well understood by those who are familiar with the lawB of 

 specific heat. 



That getting nearer to the sun as a source of heat should result 

 in pcryietual ice, is jiaradoxical at first sight ; but it is a fact, and 

 well understood by those who are familiar with the complex 

 conditions. 



The following case may or may not enter this categorj-; but after 

 much trial, I have failed to understand the conditions. 



(a.) <Jnc Oas docs not behave as a Vacuum to another. — If I trnder- 

 stand the books rightly, there is no difference between the pressoie 

 of two separate pound weights in a pair of scales, and the pressure 

 of two separate units of gas (be they similar or different) in an 

 exhausted vessel. In both cases, each presses with its own indi- 

 vidual pressure ; and in every case, the joint-pressure upon the sides 

 of a vessel will be exactly as the sum of the individual tensions. 



Volatile substances have different maximum points of tension, 

 beyond which they will not volatilise. A cubic inch of water at 

 100°C. will evaporate into an exhausted vessel of 1,700 cubic inches 

 capacity, and produce a pressure on the sides of 7C0 millimetres of 

 mercury (or one atmosphere) ; and if more water bo added, it will 

 not be evaporated ; while, if the pressure be increased, water in 

 proportion would be condensed. 



Such points of maximum tension for water are at 100° = 760 mm. 

 „ alcohol „ 1,697 „ 



„ „ ether „ 4,953 „ 



(b) One Gas docs hehavc as a Vacuum to another. — If I under- 

 stand the books rightly, one cubic inch of water wotdd evaporat* 

 into the aforesaid vessel, equally whether it be a vacuum, or filled 

 with air, or any other gas ; so that if the vessel were previously full 

 of both alcohol and ether vapours, their joint pressures would b© 

 6,C30 millimetres; against which the cubic inch of water would 

 evaporate ; but more slowly as the pressure increased. 



In the books these two aspects are confusedly mixed up together, 

 and perhaps a novice has not been quite clear in separately and 

 strongly stating the paradox. 



It is rather cmious that Clerk Maxwell, in his treatise on 

 '* Heat,'* while admitting that one gas may be a vacuum to another, 

 yet says nothing in justification of the second aspect. 



ECLECTICUS. 



VITALITY OF TOADS. 



• Le Union cl la laur des fla<iucs d'eau, amusingly mistranslated 

 by a daily contemporary : " the lemon and vase, port of water 

 ilaska." 



THE following passage from an old number of the "Cosmos," 

 m.iy interest those who have taken part in the discussion abont 

 the vitality of toads. It is an account of various experiments on 

 this subject, by M. Victor Legrips, of Chambon. JI. Legrips put 

 some toads in chambers hollowed in the earth to the depth of 

 sixteen inches, placing thcni on a tile, and covering them with » 

 pot. Others were immured between two discs of glass in plaster 

 cells, without access of air ; and some were imprisoned in masses 

 of mixed plaster, which touched evei-y part of them. Tho first 

 were ex.amined monthly, and exhibited no meirk of decay till towards 

 the twelfth month, their excretions being taken as nutriment. They 

 lived thus, on an average, for twenty-three months. The second 

 lot, examined through the glass, presented tho following phenth 

 mona : —Abundant excretions of the debris of insects and larvtB; 

 torpor while in darkness ; sparkling of the eye at approach of 

 light ; powerful efforts to escape ; progressive emaciation, till 

 death, which took place generally after fifty-six days. Among the 

 third class some toads were living after twenty-eight months OT 

 absolute sepulture. These facts prove that the toad can live a long 

 time without aliment or aeration ; he lived longer in the chambers 

 where his movements were unimpeded than in the cells where he 

 could hardly change his position ; but his life was very much longer 

 when ho was completely embedded in the plaster. Not being aMe 

 to move, he lost nothing; and thus it will be easily comprehended 

 that alimentation was much less necessary, and that his life, as if 

 suspended, might continue for an indefinite period. M. Lcgnps 

 states that toads are not only inoffensive, but exceedingly useful m 

 gardens, and that he is not at all surprised at the increasing com- 

 merce in these animals, who live exclusively on worms, caterpillars, 

 and insects, great and small, and are thus protectors of a host of 

 useful and ornamental plants. Market gardeners wUl find them 

 invaluable. 



