12 



KNOWLEDGE 



[January 1. 1894. 



is about three inches thick at the centre and seven-eighths 

 of an inch at the circumference. 



The flint lens corrects the crown so that the minimum 

 focus will be at about wave-length 561. 



For photographic work with the spectroscope in the blue, 

 violet and ultra-violet, a small lens wiU be used near the 

 focus for correcting the chromatic aberration at the centre 

 of the field only. Dr. Huggius has used such a lens with 

 his visual objective, and succeeds in bringing the spectrum 

 from F to H satisfactorily to focus. The spectroscope thus 

 remains in its ordinary position, while in the Lick telescope, 

 when the photographic correcting lens is placed over the 

 objective, the focus is changed from fifty-seven feet ten 

 inches to forty-seven feet ten inches, and in practice the 

 spectroscope is not used when the corrector is in place. 

 The principal advantages of the small correcting lens are : 

 (1) small loss of light from absorption ; (2) no change in 

 the principal focal plane ; (3) convenience in handling ; 

 (4) its weight is so small that no change in the balancing 

 of the telescope is necessary on adding the corrector. Its 

 chief disadvantage is that a small lens so near the focus 

 only gives a small field of view, but this is immaterial for 

 stellar spectroscopy. 



The telescope, dome and shutter will be moved by 

 electric motors controlled by buttons on a key-board at the 

 eye end, but the motions can also be directed from the 

 balcony at the head of the telescope, and from a table in 

 the observing room. 



Hydraulic rams, which can also be controlled electrically 

 in the same manner, will lift or lower the whole floor of 

 the observatory, so that no observing ladders will be 

 necessary. 



The clamps of the telescope are operated by powerful 

 electro-magnets, and it has been found that the instrument 

 can be instantly clamped much more firmly than in a 

 longer period by hand. 



The driving clock, which weighs about one and a half 

 tons, is never allowed to run down, but when the weight 

 has descended to a certain point it automatically starts an 

 electro-motor, which winds the clock up again. 



All the motions, clamps, &c., can be operated in the 

 ordinary way by hand. 



The dome for the Yerkes telescope will be eighty feet in 

 diameter, and the observing shutter will be fifteen feet wide. 



The tube for the Yerkes telescope is forty-two inches in 

 diameter at the objective end, fifty-two inches at the 

 centre, and thirty-eight inches at the eye end. The sheet 

 steel forming the tube varies from 7-3'A inches in thickness 

 at the centre to 1-8 inches at the ends. The total weight 

 of the tube is six tons. 



The declination axis carrying the tube is of forged steel, 

 twelve inches in diameter and twelve feet long ; its weight 

 being one and a half tons. It runs in segmental bearings 

 in the declination sleeve, which weighs four tons. 



The polar axis carrying the whole system is of forged 

 steel, fifteen inches in diameter at the upper bearing and 

 twehe inches at the lower bearing, and weighs three and 

 a half tons. 



The great weight of the bearings on these axes is almost 

 wholly relieved, and the resistance changed from sliding 

 to rolling friction by means of three bracelets or live rings 

 of steel rolls. One of these encircles the declination axis 

 near the tube, and one is placed above each bearing on 

 the polar axis. These anti-friction live rings are pressed 

 against the axes by means of adjustable springs. 



The pier or column is made in five sections. The base 

 section weighs about eighteen tons, the other sections 

 weigh about five and a half tons each. 'I'he height of the 

 column from base to top is thirty-one feet four inches. 



Each section of the pier is above six and a half feet high. 

 The head of the pier is of cast iron, in one piece, and 

 weighs five and a half tons. The total weight of the 

 pier and head is about forty-five tons. The height from 

 the base of the pier to the centre of motion is forty-three 

 feet six inches, and the total weight of the whole telescope 

 and mounting will be about seventy-five tons. 



Mr. Yerkes has purchased about fifty acres of land on the 

 borders of Lake Geneva, Wisconsin, as a site for the new 

 Observatory. The plans for the building are now being 

 prepared and its construction will be commenced in the 

 spring. The Observatory will be about one hundred and 

 fifty feet above the lake, and at a distance of about 

 seventy-five mOes from Chicago. Prof. Hale has been 

 appointed Director of the Observatory, and Mr. Burnham 

 has recently been appointed Professor of Practical 

 Astronomy in the University of Chicago and Astronomer in 

 the Yerkes Observatory. No other members of the stafi" 

 have as yet been appointed. With two such exceptionally 

 able astronomers, one may confidently look forward to 

 many important discoveries being made on the borders of 

 Lake Geneva. 



The size of Knowledge will, fi-om the commencement of 

 this year, be increased by the addition of four pages. 



Notation for the Lines of the Hydrogen Spectrum. — 

 Prof. H. C. Vogel has recently suggested (Astr. Xach. 

 3198) a slight change in the notation for the lines of the 

 hydrogen spectrum, which wUl do away with a present 

 cause of confusion. The four lines in the visible portion 

 of the spectrum, C, F, " near G," and h, have long been 

 known as Ha, H^, Hy, and Ho. When Dr. Huggins 

 discovered the series of hydrogen lines in the ultra-violet 

 region of the spectra of white stars, he distinguished 

 these by the letters of the Greek alphabet, beginning with 

 the line at A 3889 as a. From the first it was extremely 

 probable that these lines were due to hydrogen, but now 

 that their origin is definitely established, the occurrence 

 of a double a and p, itc, in the series is a decided 

 inconvenience. Prof. Vogel therefore proposes, and Dr. 

 Huggins supports his proposition, to call the fifth hydrogen 

 line, formerly known as H or Hj, He ; and the first line of 

 the Huggins series H?. AU the other lines of the 

 Huggins series will thus be advanced five steps in the 

 Greek alphabet, and the line A 3704, formerly known as i, 

 will now be HJ. — -.., — 



A restoration of Canjphodon, one of those large mammals 

 that appear so suddenly in the lower Tertiary rocks, by 

 Prof. Marsh, appeared in the Geological Maijazine for 

 November. He controverts entirely Osborn's opinion that 

 this animal walked upon the tips of its toes with its fore 

 limbs after the fashion of the elephant, while with its hind 

 limbs it was plantigrade after the fashion of a bear. 

 Perhaps the most striking characteristic of these early 

 mammals is the minute brain, which is proportionately 

 even less than that of many reptiles and amphibia. The 

 cast of the brain case, both of this animal and its near 

 relative the Deinoceras, show a ratio of brain to skull less 

 even than that obtaining in the frog. 



The Latwet bacteriologists could scarcely be expected to 

 leave our ice alone during the terrible heat wave of last 

 summer. In the laboratory cultures from 400 to 700 colonies 

 of bacteria per cubic centimetre of melted Norwegian 

 ice were obtained, and with this distressing fact they 

 inoculated the press and produced a mild epidemic of 

 paragraphs. The advice tendered the public was to use 

 ice from distilled or sterilized water, but where is it to be 

 obtained '? 



