N(n-E.MBER 1, 1889.] 



KNOWLEDGE. 



13 



tbe fall of meteoric debris, as amounting to a layer of only 

 about an inch thick in a thousand million years, an amount 

 which may he practically neglected in considering geological 

 and physical problems. His estimate is founded on Prof. 

 Newton's well-known estimate of the average number of 

 visible meteors which fall daily over the whole surface of 

 the earth, but this leaves out of consideration telescopic 

 meteors, and meteoric dust, which may fall without even 

 being \dsible in the telescope. The number of telescopic 

 meteors must be enormous compared with the number of 

 visible meteors ; for no one can observe for many hours, 

 with a low power and a field 10' or 15' m diameter, without 

 seeing several of them flash across the field. Prof. Yoimg's 

 assumption with respect to the average weight of luminous 

 meteors is founded on some observations by Thomson, of 

 Copenhagen (made thirty years ago), which connect the 

 liuninous energy of a standard candle with foot povmds. 

 The assumptions wlrich it is necessary to make in order to 

 connect the momentum of a meteor with the light it gives 

 out, as it is broken up by impact with the earth's atmo- 

 sphere, are necessarily very wide. Probably a better idea 

 as to the size of a meteoric particle capable of giving the 

 light of a sixth magnitude star may be derived from the 

 consideration that a standard candle, seen at the distance 

 of a mile, is only a little brighter than a first magnitude 

 star. Consequently, without taking atmospheric absorption 

 into account, an incandescent body, at a distance of 100 

 miles, would only appear as a sixth magnitude star if it 

 shone with a light about equal to that of an electric lamp 

 of 100 candles power. As only the larger meteors enter 

 the earth's atmosphere to a depth of below 70 miles above 

 the surface, it may be assumed that few of the meteors 

 seen, except those which appear near to the zenith, are 

 witlun 100 miles of the observer. One may, consequently, 

 pretty safely assume that a meteor which is just \isible to 

 the naked eye is larger than the portion of the carbons 

 rendered incandescent in an arc light capable of giving 100 

 candles' power. For a mass of carbon, such as is used for 

 electric lighting purposes, gives ofl' more light while being 

 driven into vapour than other substances which have been 

 experimented upon ; and the carbon of the electric light is 

 not exposed to the tremendous bombardment of cold air, 

 which must tend greatly to accelerate the disintegration of 

 the meteoric masses in their passage through the air, as 

 well as to cool their surface by removing the incandescent 

 matter as rapidly as it is formed. Added to this, Prof. 

 Newton's estimate of the average number of visible meteors 

 which fall in a day, is made on the assumption that an 

 observer at any station can see meteors which fall at a dis- 

 tance of 300 miles. 



It would be an advantage if in future editions Professor 

 Young would give more references to the places where the 

 original papers referred to may be found. In many 

 instances it is difficult, with the aid of the Koyal Society 

 Catalogue, to trace the nunioirs referred to, and hi the 

 case of many investigations by American observers it is 

 impossible from the mere name of the author to trace the 

 paper referred to. The book is well illustrated, and in 

 most instances the diagrams are original and well con- 

 trived. With all the advances that America has made, 

 authors have more to contend w ith in the land of Franklin 

 then they have here. The number of printer's errors must 

 have been very annoying to Professor Young. This has, 

 however, been greatly improved in the second edition. 



Professor Young is an accomplished practical astronomer, 

 and a teacher of great experience, as well as a popular 

 exponent of science in lucid and simple language. He is 

 also a man of wide reading, and the combination has 

 given us an astronomical text-book of exceptional value. 



A Hand-book of Descriptive and Practical Astronomy. By 

 George F. Chambers, F.R.A.S., Baiiister-at-Law, &c. &c. 

 (Printed at the Clarendon Press, Oxford, 1889.)— We have 

 received the first instalment of a Fourth Edition of tliis 

 useful hand-book, wliich has now so grown in bulk that it 

 will occupy three large octavo volumes, which will be sold 

 separately. The first volume now published is devoted to 

 the Sim, the Planets, and Comets. The second volume, 

 which it is hoped will be published at the end of this year, 

 will be devoted to '• Instruments and Practical Astronomy " ; 

 and the thu-d, which will probably appear in 1890, will refer 

 to the Stars and Nebulaj. The valuable chapters on 

 comets and the list of cometary orbits and other cometary 

 statistics given in former editions have been brought up 

 to date, and materially enlarged and improved upon. There 

 is no other work puiilished in England which contains so 

 many cometary statistics and so much infonnation with 

 respect to the forms of cometary envelopes and jets. The 

 chapters on meteoric astronomy and aeroUtes have been 

 revised by Mr. Demiing, and will well repay careful 

 perusal. In the chapter on total solar eclipses, Mr. 

 Chambers has reprmted the most important parts of Mr. 

 W. H. Wesley's valuable paper on the structure corona, 

 wliich was first published in the Monthhj Xctin's. Jlr. 

 Wesley has brought the review of coronal photographs up 

 to date for Mr. Chambers, and has given outline di-awings 

 of coronal photographs fi'om 1851 to the eclipse of 1887. 

 This affords a wider field for comparison than has hitherto 

 been laid before the public. 



The Story of a Tinder- Bo.i: By Ch.\s. Mey.mott Tidy. 

 M.D., M.S., F.C.S., &c. (Society for Promoting Chiistian 

 Knowledge. 1889.) This is a delightful little book, 

 written in the plainest untechnical language. It is stated 

 to be a reprint of holiday lectures delivered to young 

 people (evidently at the Royal Institution, though the 

 place of delivery is not mentioned). The book contains 

 a great deal of information with respect to the history of 

 matches, tinder boxes, flints and steels, D&\j lamps, and 

 such common things. Dr. Tidy seems to have been very 

 fortunate in bringing together for his audiences a collec- 

 tion of tinder-boxes, old " Sulphiu- matches," " Chemical 

 matches," which were invented in 1807 ; they were 

 tipped with a mixture of chlorate of potash and sugar, 

 and were fired by dipping them in a bottle containhig 

 asbestos moistened with sulphuric acid. The original 

 " Lucifers," invented in 1826, which were tipped with a 

 mixture of chlorate of potash and sulphide of antimony, 

 and were lighted by drawing them through a little jiiece of 

 folded glass paper; " Prometheans," and other early forms 

 of matches. The tinder-box, however, seems to have held 

 its own till 1838, when it was discovered that liones could 

 be made to yield large quantities of phosphorus at a cheap 

 rate. Up to that time phosphorus (which had been dis- 

 covered more than a century and a half previously) had 

 been sold at 50s. an ounce. The phosphorus match im- 

 mediately came into general use, and the reign of the 

 tinder-box ceased about four years before the reign of Queen 

 Victoria began. 



Timber and Some of its Diseases, By H. JIarsuall 

 Ward, F.E.S. (Macmillan & Co.) — About eighteen months 

 ago Prof. Marshall ^\■ard contributed to Xature a series of 

 articles on certain diseases of timber produced by parasitic 

 fungi, and these have been expanded into the present 

 volimic of some 280 pp. The book practically consists of 

 two parts, the first treating of the structure and classifica- 

 tion of timber and the method of its foniiation and growth, 

 and the second dealmg specially with fimgoid parasites by 



