138 
DR. T. R. ROBINSON AND MR. T. GRUBB’S DESCRIPTION OF 
assist in the annealing. It has been used thus three times, and has sustained no injury, 
nor even oxidation of its surface. 
To provide the hole required in the centre of the Cassegrain speculum, a core prepared 
in the usual manner, 7 inches diameter, was attached to a stout bar of iron extending 
across the hoop-ring, and clamped to it before pouring.] 
On July 2, 1866, the casting of the first speculum was commenced. At 1 p.m. the 
crucible was set in its place, and the furnace filled with fuel was lighted at the top, and 
cautiously heated. At 2 a.m. on the 3rd the crucible was at a full red heat, and the 
charging of it commenced. The alloy, broken into small pieces, was supplied slowly, so 
as not to risk cracking the cast iron by sudden cooling of it. By noon about 7 cwt. was 
fused ; but the furnace, which up to this time was partly fed with compressed peat, 
became choked, and the heat was much lowered. By energetic poking, feeding with 
large coke, and adding an extempore couple of feet to the chimney-shaft, the whole 27 
cwt. was fused by 8 h 30 m p.m. During the last hour the mould, which had been heated 
on the hearth A till blue, was transported by the crane to its place and carefully levelled ; 
its surface was washed with kaolin to prevent the alloy from adhering to it. 
The oven, which had been for three weeks fired with a mixture of coke and peat both 
in its flues and chamber, so that its interior was at a full red heat, was raked out in the 
chamber, and the flues were closed. 
All being ready, and the mould covered with a disk of sheet iron to keep out any dirt 
that might fall into it, the crucible was lifted by the crane from the furnace and trans- 
ferred to the cradle. The tackle of the crane was now shifted from the crucible to the 
cradle, and the former tilted until the metal reached its lip ; the metal was once more 
stirred with a birch pole and skimmed, the cover, which during these operations had 
protected the mould, was removed, and by rapidly turning the winches of the crane the 
pouring was effected in six seconds — too quickly as it seemed, for from 15 to 20 lbs. of 
the metal splashed over the opposite wall of the mould. When sufficiently cool (which 
was tested in Lord Rosse’s manner by tapping with an iron rod), the central core was 
removed, and the speculum still on the bed of hoops was drawn to the oven’s mouth. 
This was effected by a powerful crab, placed outside the building, acting on a chain and 
bar passed through the opposite side of the oven, and hooked into a large stirrup attached 
to the trunnions of the bed of hoops. The latter was now close to a step formed at the 
oven’s mouth, and the bottom of the speculum was on a level with the oven’s bed. The 
stirrup being now removed from the trunnions of the bed to those of the loam-ring, 
this, with the included speculum still red-hot, was drawn to the centre of the oven, 
leaving the bed of hoops behind. There was great difficulty in effecting this ; and all 
the appliances provided failed at first to separate them, though a pull of at least two 
tons was exerted, aided by blows given to the mould with a large piece of wood. At 
last they were started by one of the party jumping on the chain while it was so tightly 
strained. The cause of this difficulty, which had well nigh prevented the speculum from 
being drawn into the oven in time, was soon discovered. The loam-lining of the hoop 
