214 



KNOWLEDGE 



[September 1, 1890. 



In conclusion, may I point out that the narrow band of 

 increased brightness, round the limb, so well seen in the 

 photographic prints in KxowxEDdE of October last, would 

 more probably be due to light reflected to us from clifl's 

 than hill-tops. If the hills were flat-topped especially, the 

 light would (at full moon) be reflected from, and not 

 towards, our earth ; and it is because this band is so well 

 seen at full moon that I take it the light comes from cliff- 

 faces, or the slojici of hill-tops. 



Sibsagar, Asam, India, S. E. Peal. 



July 21, 1890. 



[It certainly cannot be said that most of the rays join 

 volcanic centres — Mr. Peal's theory would not apply 

 unless they all did. As to the air only issuing fi-om deep 

 clefts in the soil by reason of underground explosions, 

 one would expect to find convection currents constantly 

 in action bringing warm air to the surface over a vertical 

 vent when the walls at the bottom are warm compared 

 with the rocks above. I agree with Mr. Peal as to the 

 sides of the mountains being visible on the moon's limb, 

 and did not intend to suggest that we looked vertically 

 down on the mountain-tops. The narrow band of bright- 

 ness seen on the moon's limb shows that the higher parts 

 of the mountains with their sloping sides and cliffs are all 

 whiter than the lower gi'ound. This must either be due 

 to their natural colour or to snow. The snow-caps would 

 no doubt descend in the form of glaciers, as they do upon 

 the earth, lea^'ing the mountain-tops bare, if the snow 

 were not continually replaced by aqueous vapour carried 

 upward in the thin lunar atmosphere. — A. C. R.] 



To the Editor nf Knowledge. 



Dear Sir, — Is the following of sufficient general interest 

 to warrant an answer in your columns ? Supposing a fast 

 and a slow ball to be hit in cricket with equal force, and 

 in exactly similar manner, back over the bowler's head, 

 which will travel farther ? I have maintained that as 

 there is a' greater impetus to be overcome before the fast 

 ball commences its return journey, the distance it is carried 

 will be less than in the case of the slow ball ; but I can 

 find hardly anyone to agree with me, my opponents gene- 

 rally basing their opinions on '• observation." Some of 

 them attempt to account for what they believe they have 

 observed, by remarkmg that the elasticity of the bat woidd 

 drive back a fast ball farther than a slow one. I should 

 like to have a disinterested theoretical opinion about it, 

 if you do not consider it outside the scope of your maga- 

 zine. Apologising for troubling you, 



I am Sir. vours faithfuUv, 



St. Leonard's. " W". W. E. 



[" W. W. E." does not give all the data that are neces- 

 sary to answer his question. E\erybody is familiar with 

 the fact that a slow ball rebounds to a less height from a 

 floor than a ball thrown down more rapidly, and the fact 

 is not aff'ected by the floor being elastic as well as the ball. 

 Consequently, if the ball were " blocked " by the batsman 

 firmly holding the end of his l)at on the ground, the fast 

 ball would return fastest, and the velocity of return would 

 bear a constant ratio (depending on the elasticity of the 

 bat and the elasticity of the ball) to the velocity with 

 which the ball was delivered. When the ball is struck in 

 the usual manner, the velocity of the bat will be most 

 reduced by the fast ball at the instant when the ball is 

 reduced to rest, as well as at the instant when the ball 

 leaves the bat, if there is no muscular force applied to the 

 bat in the interval ; but we must know the weight of the 

 bat as compared with the weight of the ball, as well as 



the way in which the force of the batsman's arm is 

 applied — as he continues to urge the bat forward after the 

 ball has been reduced to rest — before we could attempt to 

 calculate the velocity of the return of the fast ball, as 

 compared with the return velocity of the slow ball. It is 

 e%'ident that a fast ball would be returned more rapidly, 

 fi'om a pendulum weighing some tons, than a slow ball 

 which hit the pendulum in exactly the same part of its 

 swing. But from a pendulum so light as to be nearly 

 reduced to rest by the blow of the fast ball, the slower ball 

 would return most swiftly. — A. C. R.l 



Messrs. Longman and Co. wish me to state that the 

 publication of the parts of the Old and Xeiv Astmnomy has 

 not come to an end. Part XI. has occupied me much 

 longer than I expected. I am, however, now at work upon 

 the last sheet of it, and hope to pass it for press in the 

 course of the next week. Part XII. and the Index will, 

 I hope, follow shortly. 



We learn from a Californian paper, which ^Irs. Proctor 

 has forwarded to us, that some citizens of San Diego pro- 

 pose to found a Proctor Memorial Observatory on the 

 summit of Mount San Miguel, a mountain peak overlook- 

 ing the town of San Diego. Mrs. Proctor writes to us fi-om 

 the Lick Observatorj-, where she has been stopping as a 

 guest of Mr. Burnham, after completing a successful lec- 

 turing tour in California. 



A star showing a bright line spectrum which difl'ers from 

 that of any other star showing bright lines has been dis- 

 covered at Harvard. It is of the 9-3 magnitude, and its 

 position is R.A. 19h. 31 -gm., decl. + 30° 19'. 



Xotirrs of Boofes. 



A HandbooJ; of Dexcriptite and Praetiral Astronomij, 

 Vols. II. and III. By Geor«e F. Ch.ambers, F.R.A.S., 

 Oxford Clarendon Press. Volume II. deals with astrono- 

 mical instruments — the telescope and its accessories, 

 telescopic stands, transit instruments, and the forms of 

 observatories. A valuable history of spectroscopic astro- 

 nomy, which has been re%ised by Mr. Maunder, occupies 

 nearly a himdred pages. Volume III. is devoted to stellar 

 astronomy, and contains a very great number of valuable 

 lists and references, ilr. Chambers has always made the 

 compilation of such hsts and catalogues a feature of his 

 books ; and they greatly add to the value of this book as a 

 work of reference. His list of large achi-omatic telescopes, 

 his bibliography of star catalogues, and his chronology of 

 astronomical discoveries, in the second volume, are all verj- 

 valuable. Unfortunately the printers have made some 

 strange mistakes in printing the third volume, ha^^ng 

 intermixed the catalogue of Red Stars and the catalogue of 

 Binary Stars in a way which must be very annoj-ing to the 

 author. Part of the catalogue of Binary Stars seems to 

 have been left out, and part intermixed with the Red Star 

 chapter. Page 321 is followed on the other side of the 

 leaf by page 290. 



JJirdu' Xests, F.iiijs, and Eiifi CoUectini/. By R. Kearton. 

 (Cassell & Co.) This is a most attractive little book, 

 clearly printed, and very tastefully got up. Of the plates 

 it is impossible to speak too highlj' ; the}- are models of 

 colour printing, and are both artistic and natural. There 

 are sixteen of them, each representing nine eggs, so that 

 about half the British species are figured. In his intro- 

 ductory remarks, Mr. Kearton teaches the egg collector to 



