July 20, 1883.] 



♦ KNOWLEDGE ♦ 



39 



the space on the heavens occupied by the sun, supposed 

 vertical) to half the area of the whole sphere, or the ratio 



108 : 10,000,000 

 or 1 : 92,592. 



If we suppose the disc replaced by a smooth spherical 

 moon, we must increase 92,592 in the ratio of 3 to 2, 

 getting the ratio 



1 : 138,888. 



Now, the actual quantity of light received " from the 

 moon is about 1,618, 000th of the sun's light, or less than 

 the 92,592nd part in the ratio 



92,592 to 618,000, 

 which would give the moon's reflective power (on the 

 assumption of her reflecting as a flat disc, and of her disc 

 being as large as the sun's), the value 

 92,592 . 

 618,000 ' 

 but taking into account the smaller mean disc of the moon, 

 we deduce the value 0-16 approximately. Taking the 

 moon as a smooth sphere, we obtain the value 2 4. Now, 

 Zollner gives the value 0-1736, which is much nearer the 

 former than the latter value. This is what, following 

 Lambert, he calls the idbp-do, or whiteness of the moon ; 

 and he justly remarks that, taking her whole brightness, 

 the moon must be regarded as more nearly black than 

 white. But he adds that from his estimates of the illumi- 

 nation of the moon's brighter or brightest parts, he is 

 satisfied that their whiteness can be compared with that of 

 the whitest of terrestrial substances — or, to use his own 

 words, he has arrived at the result " dass der Mond an 

 seinen helleren und liellslnH stellen aus einem Stofle besteht, 

 der, auf die Erde gebracht, zu den weissesten der uns 

 bekannten Ktirper geziihlt werden wiird." 



Zollner gives the following determination of the albedines 

 or tvhitenesses of diflerent terrestrial substances : — 



By diffused reflected light — 



Snow just fallen 0'783 



White paper O'TUO 



White sandstone 0'237 



Clay marl O'lSG 



Quartz porphyry O'lOS 



Moist soil 0-079 



Dark gray syenite 0-078 



By regular reflection^— 



Mercui-y 0-G48 



Speculum metal 0-535 



Glass 0-040 



Obsidian 00.32 



Water 0-021 



It will be noticed how closely Zollner's result accords 

 with the statement of Sir John Herschel that the moon's 

 average I)rightn(!ss does not exceed that of sandstone. 

 "The actual illumination of the lunar surface is not much 

 superior," Herschel says, " to that of weathered sandstone 

 rock in full sunshine. I have frequently compared the 

 moon setting behind the grey perpendicular farade of the 

 Table Mountain, illuminated by the sun just risen in the 

 opposite quarter of the horizon, when it has been scarcely 

 distinguishablf! in lirightness from the rock in contact with 

 it. The sun and moon being nearly at equal altitudes, and 

 the atmosphcn^ pc-rfcctly free from cloud or vapour, its 

 ellect is alike on both luminaries." 



It follows, of course, that since the brightest portions of 

 the moon's surface are four or five times as bright as her 

 average or mean illumination, the darkest portions are very 

 much less bright tiian the average. We may assume that 

 the floor of Plato, for instance (not absolutely the darkest 

 part of the moon), is considerably darker even than dark 

 grey syenite. 



(To be continved.) 



ARE COPPER SALTS POISONOUS? 



To most readers this will seem a foolish question, as from 

 one generation to another people have been warned 

 against pickles made green with copper salts, putting half- 

 pence into the pot with peas or cabbages to ensure their 

 coming to table with good complexions, and against cook- 

 ing anything in copper vessels without special precautions 

 to prevent the metal from being acted upon. It is hard to 

 believe that all these warnings have been unnecessary, that 

 so far from copper salts being mischievous, they can do no 

 harm in the quantities likely to be found in food in con- 

 sequence of the practices mentioned, and may even be of 

 prophylactic use to the persons swallowing them. About 

 a year ago a number of French doctors took copper-tinted 

 peas and similar articles under their protection, and at the 

 same time advocated the greatest care in keeping lead salts 

 out of the way. They considered it very dangerous for 

 tinned vessels intended to hold preserved meats or vege- 

 tables to be soldered inside, as the lead of the solder -vv-as 

 likely to be acted upon, and even in very small quantities 

 the lead salts would be dangerous. Copper salts are dis- 

 tinguished from lead salts in having no cumulative action 

 upon the system, and symptoms of poisoning do not follow 

 their repetition in minute doses, as they do in the case of 

 lead. As a practical question, it is contended that the 

 employment of copper as a food colouring agent ought not 

 to be treated as an adulteration dangerous to health, and 

 a decision in Belgium has been lately reported founded 

 upon this view. 



M. A. Gautier has recently published a work on "Copper 

 and Lead in Alimentation and Industry," and his state- 

 ments regaiding the former metal coincide with those of 

 previous "French inquirers. He speaks of the presence of 

 copper as a normal ingredient in many articles of food, such 

 as wheat, barley, rice, beans, cofiee, itc. The quantities in 

 these cases are infinitesimal, but capable, in some instances, 

 of producing a noticeable effect upon the creature swallow- 

 ing them, as in the interesting case of the Turacous, whose 

 fine red feathers Professor Church discovered to be coloured 

 with a compound he named turacine, which was soluble in 

 soft water, and contained a portion of copper derived from 

 the fruits on which the birds feed. 



M. Gautier finds in the articles of food above mentioned 

 from four to ten milligrammes per kilogramme* of copper. 

 Preserved aliments, such as vegetables and fruits, with 

 copper " verdure clad," contain more of that metal — froni 

 ten to 200 milligrammes per kilogramme. Five milli- 

 grammes a day he reckons to be about the quantity com- 

 monly taken, and no inconvenience results from it. Choco- 

 late is amongst the articles which, contrary to what might 

 be expected, appear to contain a maximum of copper. The 

 strong and repulsive flavour of copper salts limits the 

 quantity anybody would be willing to swallow. When food 

 is dosed with four grammes (over 61 grains) per kilo- 

 gramme, it is too nasty to eat ; but even then Jl. Gautier 

 affirms it would not be dangerous to take. Copper salts 

 soon act as an emetic, unless the quantity is small, and, 

 according to the new \-iews, poisoning by them is almost 

 impossible. These opinions are founded upon experiments 

 French doctors have made upon themselves and their 

 friends. Dr. Galippe as far back as 1875 tried copper salts 

 upon various animals, and acquired so much confidence in 

 their innocence that he proceeded to take and give verdigris 

 to his family and acquaintances without any mischief 

 ensuing. 



* The milligramme is -0154 of a gi-ain; the kilogramme 21b- 

 3 oz. 5 drams, or 15-44rlO-2344 grains. 



