136 Progress in Science. [January, 



M. Bauer, of Gottingen, has, therefore, proposed to distinguish the Australian 

 mineral as Seebachite — a name complimentary to Professor Karl von Seebach. 

 At the same time, it must be confessed that the composition of the two minerals 

 may perhaps be eventually reduced to a general formula, in which event a 

 relation might be traced between herschelite and seebachite similar to that 

 which obtains between natrolite and mesolite. 



A curious instance of the occurrence of hemimorphism in a crystal of calc- 

 spar — perhaps an unique example — has also been described by Bauer in the 

 Zeitschrift of the German Geological Society. The specimen in question 

 occurs in a group of crystals of calcite from Andreasberg in the Hartz — a 

 locality well known to the mineralogists for the beauty of its crystallised 

 calcite. Most of the crystals in this group are attached by one end to the 

 matrix, and hence it is impossible to compare the characters of the two ex- 

 tremities ; but it happens that one crystal has curiously grown across another 

 in such wise that the two ends of the former crystal are free, and hence admit 

 of observation. The hemimorphism consists in one end being terminated 

 simply by the fiat basal plane, whilst the other extremity exhibits a compli- 

 cated set of rhombohedra and scalenohedra. As the occurrence of hemi- 

 morphism is usually correlated with pyro-electric properties, the crystal of 

 calcite was heated to 150 C, but without any development of electricity. 

 Exposure to a higher temperature was forbidden by fear of damaging so inte- 

 resting a specimen. 



Mr. C. Horner has communicated to the " Chemical News " a short note, 

 announcing the discovery of the rare metal didymium in a specimen of pyro- 

 morphite, or phosphate of lead, from Cumberland. 



Dr. Gladstone, F.R.S., has succeeded in preparing microscopic specimens of 

 filiform silver, strongly resembling the characteristic threads of the native 

 metal well known to mineralogists as occurring in calcite at Kongsberg in 

 Norway and in Chili. The artificial specimens were reduced from a solution 

 of nitrate of silver by suboxide of copper, and it is suggested that the native 

 silver may have been reduced by a similar reaction in nature. 



ENGINEERING— CIVIL AND MECHANICAL. 

 Guns and Armour. — The results of the Glatton-Hotspur experiments re- 

 corded in our chronicles of last quarter have recently come under discussion 

 at Portsmouth by the Naval Professional Association, on the 1st November 

 last, when a paper on the subject was read by Commander W. Dawson, R.N. 

 From this paper it appears that the defeat of the gun by the turret was in 

 strict conformity with well-known mechanical principles, with previous 

 Shoeburyness experiments, and with Woolwich calculations. The shots fired 

 at the Glatton were from a 12-inch 25-ton gun, rifled on the French or 

 Woolwich system, and the results of the firing fully confirmed Captain Hood's 

 remark as to the well-known "inaccuracy of flight now observed in a 12-inch 

 gun of 25 tons at very short ranges." Now, from a diagram published by 

 Mr. N. Barnaby, the Chief Naval Architect, it appears that the force required 

 to perforate the front of the Glutton's turret, at right angles, with a 12-inch 

 projectile, is 7378 foot-tons. This would be exerted at 200 yards (the distance 

 in question) by a 600 lb. shot, which left the gun at the rate of 1357 feet per 

 second ; or by a 700 lb. shot projected with an initial velocity of 1252 feet. 

 But the 600 lb. shot actually employed, having those short stud rifle-bearings 

 which, it is officially stated, have " decidedly the lowest velocities," left the 

 gun with only 1300 feet velocity ; and, travelling 23 feet per second slower at 

 200 yards distance, it struck the turret a blow of only 6788 foot-tons. In 

 order that this projectile should perforate the front of the Glatton's turret, it 

 must leave the gun with 1357 feet velocity, or with 57 feet greater initial 

 velocity. The same object might be attained by propelling a 700 lb. projectile 

 from the same gun with 105 feet less velocity than that requisite with a 600 lb. 

 shot. Without following Commander Dawson through his proofs and argu- 

 ments, in which he clearly traces the defeat of. the gun to the defective 



