July 19, 1906] 



NA TURE 



281 



iVinting Department, Cairo, 1905 ; for the Ministry of 

 Finance). The dark outer fihii is similar to that well 

 recognised as a characteristic of stones in deserts. The 

 desert-film has been examined separately, and Mr. Lucas 

 agrees with Walther that " the colour is much the darker 

 the more the silica content of the rock." " The depth of 

 colour is dependent upon the amount of black oxide of 

 manganese in the film, and this is conditioned first by the 

 manganese content of the rock, and secondly by the oppor- 

 tunities presented for the manganese salts to be brought to 

 the surface and oxidised." " A hot climate and a small 

 rainfall are necessary to the formation and preservation of 

 the film." In regard to the river-film, it is noted that 

 certain incised stones at the First Cataract are equally 

 black on their surface and in the hollows of the inscrip- 

 tions. Silica is one of the minor constituents of the river- 

 film, but is absent from the desert-film. Mr. Lucas, after 

 discussing previous literature and his own analyses, con- 

 cludes that the river-film arises from material in the rocks 

 themselves, as in the case of the analogous desert-film. 

 Dr. W. F. Hume contributes a description of the micro- 

 scopic characters of the rocks examined, with the general 

 result that no connection can be established between the 

 surface-film and any special decomposition in the outer 

 layers. 



The June number of the National Geographic Magazine 

 contains an account of a visit to Vesuvius after the erup- 

 tion of .April 8. The account is illustrated by a number 



of reproductions from photographs, of which we reproduce 

 one showing the aspect of the cone after the eruption. 

 The scoring of the slope of the cone is due to slipping of 

 the loose ashes, not to stream action. 



The current number of the Home Counties Magazine 

 contains an interesting article on old pewter by Mr. H. M. 

 Cooke. In a broad sense pewter is composed of tin alloyed 

 in varying quantities with antimony and copper ; lead, 

 bismuth, and zinc are sometimes also employed. The 

 variety and constant change of colour are due to the 

 difference of alloys and to atmospheric influence. The 

 colour is in some measure dependent on the surface being 

 good. As a domestic article, pewter succeeded wood, and 

 was used almost universally until earthenware became 

 cheap. It did not come into general domestic use until 

 the seventeenth century. On account of its fusibility 



pewter was used by goldsmiths to lake castings of certain 

 articles. Benvenuto Cellini is said to have used it for this 

 purpose in connection with his work. It appears from Mr. 

 Cooke's article that dealers nowadays, to enhance the value 

 of their wares, often point to the small marks in shields of 

 a lion rampant or a leopard's head crowned, and describe 

 articles bearing these as "silver pewter." But such marks 

 indicate no special value in the metal, and e.xcept for the 

 infinitesimal quantity that there may be in the lead em- 

 ployed, it is safe to assume that old pewter contains no 

 silver. 



In a paper on the rapid measurement of geodesical bases 

 published in part i. of the Bulletin of the French Physical 

 Society, Dr. C. E. Guillaume gives details of the construc- 

 tion and use of the standards and measuring wires referred 

 to in his article on invar (Nature, vol. Ixxi., p. 138). An 

 account is given, in particular, of the r^pid, direct measure- 

 ment of base lines by means of stretched wires of invariable 

 length. This process is extremely rapid as compared with 

 older methods ; in good country, ten or twelve men can 

 measure up 5 to 6 kilometres per day, whereas with a 

 bimetallic scale fifty men are required, and the distance 

 covered per day does not exceed 400 metres. Formerly the 

 number of bases directly measured was kept as small as 

 possible, nearly all the values being obtained by triangu- 

 lation. The use of these measuring wires of invariable 

 length affords a means of controlling the older data, and 

 will change the character of future surveys by increasing 



the number of direct data at the 

 __ expense of those obtained by tri- 



angulation. 



The third volume of the contribu- 

 tions from the Jefferson Physical 

 Laboratory of Harvard University 

 for the year 1905 has been received. 

 The previous volumes were de- 

 scribed at some length in Nature 

 for March i last (vol. Ixxiii., p. 427). 

 The results of the investigations 

 published in the present volume were 

 obtained largely by the aid of the 

 Thomas Jefferson Coolidge fund for 

 original research. Nine of the 

 twelve papers have already appeared 

 in the Proceedings of the American 

 Academy, and most of the contribu- 

 tions have been dealt with already 

 in notes published in these columns. 



The Electrician Printing and Pub- 

 Ltd., is issuing a new series of 

 Electrician primers at 3d. each, post free. A complete 

 list of the primers will be sent on application. From an 

 examination of specimens dealing with thermopiles. 

 Rontgen rays and radiography, influence machines, the 

 induction coil, the magnetic properties of iron and elec- 

 trical units, it is clear that the series will prove of service 

 to technical students. 



The edition de luxe of the Great Eastern Railway Com- 

 pany's handbook, " Summer Holidays," by Mr. Percy 

 Lindley, is provided with an excellent series of facsimiles 

 of water-colour drawings of places of interest in the eastern 

 counties. In addition to the illustrations in colour, the pen 

 and ink drawings, the letterpress, the list of golf links, 

 and other information provided, combine to make the publi- 

 cation a useful holiday guide. 



lishing Company, 



NO. 1916, VOL. 74] 



