386 
PROFESSOR F. D. ADAMS AND DR, J. T. NICOLSON 
IV. Comparison of the Structures produced in Carrara Marble by Arti¬ 
ficial Deformation with those produced by Deformation in the case 
of Metals. 
Mugge, # whose researches in the movements set up by pressure in ice, and in 
various minerals and artificially prepared salts, are so extensive and so well known, 
in a paper read on January 14, 1899, presents the results of his investigations into 
the effect of pressure on metals and the nature of the movements resulting from it; 
and, in two papers read on March 16 and May 18 respectively of the same year, 
Ewing and PosenhainI describe a series of investigations carried out by them on 
the same subject, and which cover practically the same ground and yield the same 
results. It is pointed out that all simple metals when examined under the microscope, 
are seen to be allotriomorphic aggregates of metallic crystals, the structure being 
precisely that of a block of marble. 
When the metal is deformed by compression or tension, the effect being identical 
in both cases, the movement is found to be due to the distortion of each grain by 
slipping along gliding planes, with or without the accompaniment of twinning. This 
was observed in gold, silver, platinum, tin, copper, lead, cadmium, bismuth, antimony, 
nickel, iron, steel, and various alloys. It is in fact in this way that metals move or 
“ flow ” when submitted to pressure or impact. 
Polysynthetic twinning was found to accompany the movement on gliding planes, 
in the case of most of the metals enumerated above, both phenomena often presenting 
themselves in the same grain. 
Mugge shows that in the case of soft iron, gliding can take place along six planes, 
and that twinning is probably also developed by pressure. Ewing and Posenhain, 
in their first paper, give three photographs of the same surface of soft iron showing 
the results of progressive deformation of the constituent crystalline grains under 
pressure, which photographs could not be distinguished from those of thin sections of 
the marble described in the present paper at corresponding stages of deformation. 
In the case of a specimen of Swedish iron, strained by a pull, the width of the 
lamellae between the lines of slip was found to average 1/400 of a millim. 
Messrs. Ewing and Posenhain sum up the results of their experiments in the 
following words :— 
“ These experiments throw what appears to us new light on the character ol 
plastic strain in metals and other irregular crystalline aggregates. Plasticity is due 
to slip on the part of the crystals along cleavage or gliding surfaces. Each 
crystalline grain is deformed by numerous internal slips occurring at intervals 
* “ Ueber neue Structurflachen an den Krystallen der gediegenen Metalle,” ‘ Nachricht. der k. Gesell. 
der Wissen. zn Gottingen’; Math.-phys. Klasse. 1899. Heft 1. 
f “ Experiments in Micro-metallurgy: Effects of Strain (Preliminary Notice),” ‘ Rojo Soc. Proc., 
vol. 65; “ The Crystalline Structure of Metals,” Bakerian Lecture, ‘ Roy. Soc. Proc.,’ vol. 65. 
