SCIENCE-GOSSIP. 



3i5 



first to call attention to this effect, owing to the 

 appearance of Saturn in the three-foot mirror 

 presented by Mr. Edward Crossley to the Lick 

 Observatory. A reflector should have a focal 

 length twelve or fourteen times as great as its 

 diameter, and an object-glass from fifteen to 

 eighteen times as great as its focal length, if the 

 very finest work is to be got from it on objects 

 having an appreciable diameter. 



It is most desirable to have rack adjustment to 

 the eyepieces. Some of the poorer object-glasses 

 have a stop in the tube which cuts off the outer 

 portions of the glass from doing service. In buying 

 a telescope choose a good two and a-quarter inch 

 rather than a poor three-inch, but, consistently with 

 quality, get as large an instrument as you can. For 

 large sizes choose the Newtonian reflector rather 

 than the object-glass, because it is equal in defi- 

 nition, superior in purity of colour, much cheaper, 

 and at the same time far more comfortable to use. 

 This is because, with the Newtonian, the observer 

 is looking straight before him, even when the 

 object is near the zenith, whilst with a refractor 

 one has to lie on one's back or crane the neck in a 

 most uncomfortable manner. It is well to have a 

 good selection of eyepieces if possible. One of 

 30 or 40 diameters with a large field of view, as the 

 width of sky visible is termed, one of 60 or 70, one 

 no to 120, one of 180, and so on, according to the 

 size of the telescope. 



(To be continued.) 



Galileo's Treatise on the Tides. — The Abbe 

 Cozza Luzzi has had the good fortune to discover, 

 in the Vatican library, a manuscript, hitherto only 

 known as N. 8193, which proves to be Galileo 

 Galilei's own manuscript treatise on the tides. It 

 ends thus : " Written in Rome, in the Medici 

 Gardens, on January 8, 1616." It was dedicated 

 to his admirer, Cardinal Orsino and Maecenas. 

 The Pope, Leo XIII., has ordered the work to be 

 published. 



The Spectrum of the Great Nebula in 

 Orion. — This, like the spectra of so many nebulae, 

 consists of bright lines. There is the F line of 

 hydrogen, known as H /3, and two less refrangible 

 lines, A. 5007 and a 4959, only seen in nebulae. 

 These lines are found by Professor J. E. Keeler, 

 with the 36-inch Lick refractor, to vary in relative 

 brightness in different parts of the nebula. Near 

 a star marked 734 by Bond H # was the strongest 

 line. The bright portion near the Trapezium 

 was found to have the chief nebula line a 5007 

 much the most intense, the other two being about 

 equally bright. This seems to indicate differences 

 in the composition of different parts of the nebula. 



The Earth's Mass. — At the meeting of the 

 British Astronomical Association, held at Sion 

 College, on January 25th, Professor C. V. Boys read 

 a most interesting paper on " The Determination 

 of the Newtonian Constant of Gravitation," in 

 which he described how he measured the mass 

 of the earth. His value for this is 55270, water 

 being 10. In other words, he makes the earth 

 turn the scale at 5,882,064,000,000,000,000,000 

 tons, a result almost identical with that arrived 

 at in a different manner by the Jesuit, Dr. C. 

 Braun, at Mariaschein, in Bohemia, who, how- 

 ever, increased the fourth decimal figure from 

 o to 3. The Professor hopes soon to visit the 

 father, when he trusts that this tiny difference 

 may be righted. 



Departmental Editor. — The Editor of 

 Science-Gossip desires to thank the numerous 

 gentlemen who have, in reply to his invitation, 

 so kindly volunteered to act as Honorary Depart- 

 mental Editor for Microscopy in this Journal. 

 They will in a short time receive individual replies, 

 and it is expected that the new Departmental 

 Editor for this section will soon be announced. 



A Cheap Condenser. — A cheap and effective 

 form of condenser may be made by taking a 

 globular eight-ounce bottle with an enlarged neck 

 and mouth, and filling it with filtered water. It 

 should be well corked, and used in an inverted 

 position. If filled with a solution of ammonio- 

 sulphate of copper, it may be used in the place of 

 the blue glass chimney and condensing lens. 



Structure of the Paris Limestones. — The 

 study of the microscopical structure of the rocks 

 of the Paris Basin by means of thin sections, 

 chemical analysis and comparison of insoluble 

 residues, has enabled Dr. Lucien Cayeon to give to 

 the scientific world a most valuable and instructive 

 work bearing on the genesis and natural history 

 of the sedimentary deposits from Jurassic to 

 Eocene times. To the petrologist the results are 

 invaluable. We cannot here do more than briefly 

 refer to the general scope of the work ; but for 

 those who desire further information, we would 

 recommend a perusal of the remarks of Dr. 

 Hinde, in the October issue of the "Geological 

 Magazine." The work is illustrated with beautifully 

 executed lithographic plates of Radiolaria, enlarged 

 sections of chalk, glauconite and other minerals. 



Life Conditions of the Oyster. — We are 

 indebted to the courtesy of Professor W. A. Herd- 

 man for a copy of the report of the Committee 

 that was appointed to consider the elucidation of 

 the life conditions of the oyster under normal and 

 abnormal environment, including the effect of 

 sewage matters and pathogenic organisms. This 

 report was submitted at the last meeting of the 

 British Association. The questions of the amount 

 of copper and iron present in various kinds of 

 oysters, and of the infection of shell-fish by typhoid- 

 like organisms as well as the differentiation of 

 these from the Bacillus coli-communis on the one 

 hand and the true B. typhosus on the other, are fully 

 described and discussed. The presence of colon- 

 like organisms, in so many of the batches of oysters 

 mussels, cockles, periwinkles and whelks that were 

 examined, demonstrate the urgent need for some 

 legislation regarding the importation, laying and 

 growing of oysters, as well as periodical inspection . 

 of the beds by duly qualified scientific authorities. 

 This colon group of bacilli is frequently found in 

 " shell-fish " as sold in towns, especially in oysters, 

 but there is no evidence that it occurs in Mollusca 

 living in pure sea-water. Neither is there any- 

 thing to show that the presence of the colon 

 bacillus indicates sewage contamination. There 

 is, therefore, much more work to be done in this 

 direction, before the cause of the infection can be 

 definitely established. 



