102 Progress in Science. [January, 
chemical constitution of this group of minerals, he describes the result of his 
microscopic examination of two or three special felspars. He is thus led to 
regard the albite of Harzburg as a mixture containing 96°34 per cent of albite, 
with 3°66 of anorthite, whilst the orthoclase of Harzburg, although presenting 
the crystalline form of a potash-felspar, really contains almost one-half its 
weight of albite. The well-known orthoclase from St. Piero, in Elba, is also 
rich in soda, and specimens viewed under the microscope are seen to contain 
albite to the extent of at least one-sixth or one-eighth of the mass. It is 
needless to indicate the bearing which such facts have upon the theory of the 
constitution of the felspars as elaborated by Tschermak. 
Further information respecting the conditions under which the diamonds 
occur in South Africa have been sent to this country, and will be duly pub- 
lished in the “ Journal of the Geological Society.” Mr. Tobin, who has 
recently returned to England, has brought with him a most interesting 
specimen, exhibiting an aggregation of crystals of diamond, apparently asso- 
ciated with asmall quantity of foreign matter, which may perhaps represent 
the matrix. The specimen was found at Du Toit’s Pan, which appears to 
be the present focus of the workings. 
A mineral from Arendal, in Norway, hitherto regarded as a variety of garnet, 
has been found by M. Damour to be really an idocrase. The same chemist 
publishes the analysis of a garnet from the Rancho de San Juan, in Mexico. 
M. Daubrée calls attention to the recent discovery of masses of phosphate 
of lime in the South of France. These masses, although extremely unpromising 
in external appearance, are sufficiently rich to prompt ative search for similar 
substances elsewhere. 
In Mr. Collins’s recently published work on the Mineralogy of Cornwall and 
Devon,* we are presented with a valuable account of the many minerals found 
in our two western mining counties. The author’s position as lecturer to the 
Miners’ Association is a sufficient guarantee for the general trustworthiness of 
the book. Of course itsespecial value lies in the detailed lists of localities, but 
its interest is by no means purely local. Among the most interesting parts, 
we may point to the chapter on blowpipe reactions, and to the tabular 
schemes by which minerals are classified according to their most obvious 
physical characters. The second part of the work is really a dictionary of 
mineralogy, and contains lengthened descriptions of the species arranged 
alphabetically, and illustrated by ten lithographic plates of crystals, remarkable 
for the accuracy and clearness of their outlines. 
ENGINEERING—MILITARY, CIVIL, AND MECHANICAL. 
Guns.—In the Engineering Chronicles which appeared in the “ Quarterly 
Journal of Science,’ some reference was made to experiments carried out by 
Government between the Prussian and English g-pounder field-gun. The 
Prussian gun is known in Prussia as a 4-pounder, that being the weight of the 
round shot it carries; but asit fires a g°5 lbs. cylindrical shell, it should really 
be taken as a gun of the latter capacity. Last November, some further com- 
petitive trials were carried out at Shoeburyness between these guns; the 
practice being made against four rows of targets, each having a frontage of 
54 feet wide by g feet high, the rows being placed 60 feet apart, one beyond 
the other, thus giving a depth from front to rear of 180 feet. At a distance of 
2500 yards, the Prussian gun (breech-loader) with common shell, made in ten 
rounds a total of 144 hits, whilst the English gun (muzzle-loader) made only 
107 hits. With shrapnell shells the respective performances were, with the 
Prussian gun 125 hits, and with the English gun 312 hits. At a range of 
3000 yards, the effective performances with common shells were 21 hits and 
38 hits respectively, and in subsequent experiments with shrapnell shell, the 
* A Handbook to the Mineralogy of Cornwall and Devon; with Instrudtions for their 
Discrimination, and Copious Tables,of Localities. By J. H. Collins, F.G.S., &c. Truro and 
London, 1871. 
