Nov. 28, 1884.] 



♦ KNOWLEDGE ♦ 



443 



brush, the fingers holding the object being well provided 

 with a quantity of the powder to prevent their impression 

 being left on the article to the detriment of the silver sur- 

 face to be presently provided. When the surface is exten- 

 sive, it is very desirable that, in applying the bath-brick, it 

 should be worked as evenly as possible. It is a good prac- 

 tice to finish cleansing by rubbing the surface with a piece 

 of damp chamois leather, provided with some finely- 

 powdered bath-brick, the fingers Vjeing moved in circles. 

 In this way a tolerably smooth surface may be imparted. 

 When the bath-brick process is finished, the object is 

 thoroughly washed with clean water. Superficial im- 

 purities may bo removed by brief immersion in a solution 

 composed of equal quantities of sulphuric acid and water, 

 with a little nitric acid added. Verdigris is removed by the 

 application of a little hydrochloric acid. 



AMERICAN FOREST FIRES. 



THIS is the season for forest fires, and in many parts of 

 the country we hear of great destruction already from 

 burnt fields and forests. The New Bedford Evening 

 Standard, in an article on the subject, says : — Few 

 people realise how serious a calamity these fires have 

 become. Already in the most thickly-settled parts of the 

 country good working wood is becoming scarce and high, 

 althou^h there is often a glut of inferior grades, and there- 

 fore very low prices for them. The correspondents of the 

 lumber journals report from almost all quarters that the 

 demand for really good material is generally in excess of 

 the supply. The only hope for the future lies in economy 

 of what we have, and in whatever will encourage those 

 owning young timber to keep it and prune it, and thin it 

 out so as to bring it on to fill up the gap. But forest fires 

 destroy an amazing amount of the precious mature stock — • 

 how much no one knows — but it is said by experts that 

 the amount destroyed probably equals the amount cut. 

 Now, we know that the sawed stutj (to say nothing of 

 fuel and charcoal, ties, telegraph, and l-.op poles, kc.) 

 reaches an annual value of over 230,000,000 dols. at the 

 mills, so that, counting other forest products besides sawed 

 stufT thus destroyed, it is, no doubt, within reason to say 

 this waste, largely needless, is not less than 300,000,000 duls. 

 a year. But this is not all, and very likely it is not the 

 worst. Such fires burn up a great amount of young 

 growth and of seed, and in some cases even the soil itself 

 is roasted to death, so that for a long time afterward it will 

 not bear anything of value. 



Mr. Swan states that lie has obtained 5,800 hours as the life of 

 an incandescent lamp, and large numbers of the Swan lamps are 

 said to have reached 4,000 hours. 



We hear that a Working Man's Club and Institute is to be 

 established in connection with the Royal Victoria Coffee Hall. 

 It will be supported by the subscriptions of the members 

 (minimum Is. per quarter), and the donations of those who are 

 interested in the movement. Mr. Robert W. Bowers, of 89, Black- 

 friars-road, will furnish any information needed by those who 

 may wish to co-operate in so praiseworthy an object. 



A CnnscH Boilt from a Single Tree. — A redwood tree, cut in 

 this county, furnishes all the timber for the Baptist church in 

 Santa Rosa, one of the largest church edifices in the country. 

 The interior of the building is finished in wood, there being no 

 plastered wall. Sixty thousand shingles were made from the tree 

 after enough was taken for the church. Another redwood tree, 

 cut near Murphy's Mill, in this county, about ten years ago, fur- 

 nished shingles that required the constant labour of two industrious 

 men for two years before the tree was used up. The above state- 

 ments are vouched for as true by Supervisor T. J. Proctor. — Santa 

 Rosa {Cal.) RejytM ican . 



A TOTAL LUNAR ECLIPSE. 



By KiCHARD A. Pkoctor. 



THE recent total eclipse of the moon presented pheno- 

 mena of considerable interest ; and as usual with 

 lunar eclipses was made the subject of comments indicating 

 considerable misapprehen^^ion of the real circumstances of 

 such eclipses. So much more interest attaches to total 

 solar eclipses, that most of th<'ir phenomena are pretty 

 fairly understood ; but with lunar eclipses the case is 

 different. Thus in the case of the recent eclipse, even the 

 account given in the Times of Oct. 6, though obviously 

 written by official astronomers at Greenwich, contained 

 errors in regard to the physical phenomena of the eclipse. 

 It assigned as a reason for the darkness of the moon during 

 totality the (presumed) freedom of the earth's atmosphere 

 from vapour, which would indeed have explained the 

 absence of ruddiness, but would have left the darkness of 

 the moon during totality a greater mystery than ever. It 

 also repeated the well-worn mistake of assigning diversities 

 of illumination of the moon's disc to the passage of the sun's 

 rays " through parts of our atmosphere of different degrees 

 of saturation." Irregular diversities of illumination, such 

 as are actually observed during total lunar eclipses, cannot 

 possibly be explained in this way. 



I propose to take this opportunity to discuss the circum- 

 stances of a lunar eclipse in a new way, which possesses the 

 advantage of being simpler than the customary plan, and is 

 also more instructive in regard to the physical problems 

 involved. I take the eclipse of Oct. 4th, but any other 

 total lunar eclipse would have served my purpose equally 

 well. 



Every student of astronomy knows the usual way of 

 dealing with lunar eclipses, in which the passage of the 

 moon through the earth's shadow is considered*, and the 

 station of the observer is supposed to be on the earth, the 

 general elements of the eclipse being taken for the earth's 

 centre. Let us, instead, set our observer on the moon, or 

 for convenience at the moon's centre, and consider the way 

 in which the earth's disc would seem to pass athwart the 

 face of the sun. 



The elements of the eclipse, as given in the Nautical 

 Almanac, are obviously translatable at once into the fol- 

 lowing (only differing in taking the motion i>f the earth's 

 centre, as seen from the moon's, as the exact opposite of the 

 motion of the moon's centre seen from the earth's) : — 



Greenwich Mean Time of Conjunction in R.A., h. m. s. 



Oct. 4 10 8 5-1 



Right Ascension of Earth and Sun 12 44 2502 



Earth's Declination S 4 57 57-9 



Sun's Declination S 4 46 33-6 



Earth's Dailv Motion in R.A 34 13-5 



Sun's Hom-ly Motion in R. A 2 16-7 



Earth's Hourly Motion in Declination S 10 52'9 



Sun's Hourly Motion in Declination S _ 57'7 



Earth's Equatorial Serai-diameter 59 23'0 



Sun's True Semi-diameter (seen from Moon)... 15 50'9 



The only element here altered is the sun's semi-diameter, 

 which in the Nautical Almanac is given as 16' 2"4" : this 

 of course has to be reduced as seen from the moon ; and to 

 reduce it, we have to use the only element omitted above, 

 viz., the solar parallax, or 8"-9 ; for the moon's parallax 

 .59' 23" divided by the sun's gives the sun's distance as 

 compared with the moon's, or almost exactly as 400 to 1 ; 



* This seems the most natural and obvious way of dealing with 

 the problem ; but it gives no information as to the cause of diver- 

 sities of illumination depending on the condition of various parts 

 of that zone of the earth's atmosphere through which the sun's 

 ays are refracted towards the moon. 



