T. M. Reade—Effects of Temperature on Terra-Cotta. 27 
lengthening, as shown by movement on the corbel bricks which 
occur at intervals, was evenly distributed along a length of 380 feet. 
One of the first explanations that occurred to me was that the 
lengthening was due to the expansion of the cement, as we know 
that cement if used too soon does expand for a certain length of 
time after setting! Enquiry from the builder, Mr. Bates, who put 
up the wall, showed this not to be a probable explanation, as the 
wall was built some seven years ago. Mr. Bates informed me that 
he reset the end bricks of this portion of the coping, about two 
years after the wall was built, in consequence of its lifting, and I 
have ascertained that Mr. Taylor, a bricklayer, has reset it on two 
occasions when it lifted from the same cause, first on May 9th, 1884, 
and secondly on May 16th, 1885. He has now just reset it for a 
third time. 
An inspection of brick copings in the neighbourhood of Blundell- 
sands, of which there are many, disclosed the fact that this is not 
a solitary phenomenon. In another case where the coping is of blue 
Staffordshire bricks, the top course in cement and the under-course 
in mortar, a change in length is shown clearly by the coping being 
lifted off the wall at each of the two ramps (curved changes of 
level) which exist in its length, and the movement can be clearly 
measured on the corbel bricks as before, and in this case the lengthen- 
ing is also a quarter of an inch, evenly distributed over a considerable 
length of coping. 
Numerous other examples are to be seen, which, though not so 
striking as those described, clearly evince a movement of the copings. 
It will no doubt be considered a long step from brick copings to 
mountain-building, but as a good example of the permanent lengthen- 
ing that may take place as the accumulated result of small movements 
of expansion by change of temperature in what appears to be an 
intractable material, the facts are well worthy of record. It appears 
that when the ends of a coping such as I have described butt up 
against a solid pier, this movement does not take place probably 
from the elasticity of the material being sufficient to absorb whatever 
small expansions may occur.” When one end is partially free to 
move, the effect is different, each expansion, however small, pushing 
the coping along towards the partially free end, and on contraction 
the coping cannot draw itself back to the same position as before, 
so must either fracture or lengthen by increments, and experience 
shows that is what frequently happens. 
1 In order to ascertain precisely whether any alteration of length does take place 
in cement, I had a bar made composed of one of best Portland cement to one of 
fine sand. In this bar were fixed brass studs for measuring purposes. On Sept. Ist, 
three weeks after it was made, the bar measured 16°136 inches between the studs. 
On Noy. 6th it measured 16°122 inches, showing a shrinkage of 0:014 of an inch, 
and the contraction has not yet ceased. 
2 Since this was written I have observed several cases in which the end brickwork 
and piers have been badly fractured by the force of expansion. 
