396 
silicon in 1,000 of Bessemer steel renders it hard and 
brittle when cold. In ordinary Bessemer pig iron it is 
present in quantities varying from one to four per cent. 
The author gave it as his opinion, from experimental 
inquiries, that silicon is dissolved or “ occluded” in iron 
in the same way as carbon is, but that the solvent power 
of the metal is so much greater for silicon than for carbon, 
that it is quite a rare thing, even if it ever occurs, for 
silicon to separate in a free state from the iron; and he 
considered that the methods of mechanical separation 
which he had adopted for the investigation of the condition 
of carbon and silicon would prove effectual aids to the 
ultimate analysis of iron, and a valuable supplement to 
the ordinary methods of research. 
Mr. Isaac Lowthian Bell complimented Mr, Snelus upon 
the great value of his paper, and criticised some of the state- 
ments made in it. Onthe presence of silicon in steel, 
ir. Bessemer said that a very general opinion prevailed 
in the trade (and it was correct when they spoke of large 
quantities) that silicon was deleterious to the make ofiron. 
It was the impression that they should get rid of silicon, 
and they would then make better iron. That was not the 
case, in proof of which assertion he called attention tothe 
old steel process as carried on in Sheffield, and adduced 
instances to show that the presence of silicon improved 
the quality of the manufacture. He had not had an ana- 
lysis of the best quality of Sheffield steel that did not 
contain silicon. 
A discussion was then taken upon a paper read at 
the meeting held in London in May last, the subject 
of which was “A Method of Designing Rails,” and the 
afternoon was spent in visiting the works of the Plymouth 
Iron Company, the Castle Pit winding and pumping 
machinery, and the Cyfarthfa Iron Works, the property of 
Mr. Crawshay. At the last-named works there was seen 
an immense stock of puddled iron, upwards of 20,000 
tons, stacked in “houses,” each containing 300 tons. 
The proceedings were resumed on Wednesday morning. 
The papers read were the following :— 
I. “On a New Form of Pyrometer.” By Mr. C. W. 
Siemens, C.E. F.R.S. D.C.L. After describing briefly 
the Wedgewood and Gauntlett pyrometers, and one 
previously constructed by himself, Mr. Siemens proceeded 
to describe a pyrometer of more universal applicability. 
It is based upon the peculiar properties of the pure metals 
to offer an increasing resistance to the passage of an 
electrical current with increase of temperature. A platinum 
wire of known electrical resistance is wound upon a cylin- | 
der of fire-clay, upon which a helical path has previously 
been cut to prevent contact between the turns of the wire. 
The coil of wires, so prepared, is enclosed within a cylin- 
drical casing of platinum if the temperatures to be 
measured exceed the welding heat ; or of iron or copper, 
if lower temperatures only require to be measured. The 
two ends of the coil of wire are brought out end ways, and 
are attached within the protecting tube to thicker leading 
wires of copper, insulated for a short distance by being 
passed through pipe-clay tubes, and further on by india 
rubber or gutta percha, terminating at the measuring in- 
strument, which may be placed at any convenient dis- 
tance. The characteristic feature of this instrument is 
that the usual calculations necessary to determine elec- 
trical resistances by the Wheatstone or other methods 
are dispensed with, and a reading in degrees of a large 
scale is at once obtained by so placing the index lever 
that the electrical current, generated in a small battery 
and passed through the measuring instrument, including 
the platinum wire of the pyrometer, produces no deflec- 
tion of the galvanometer needle. The temperature whick 
these degrees represent is expressed by a table of refe- 
rence, which accompanies each instrument. The correct- 
ness of this instrumeut depends solely on the ratio of in- 
crease of electrical resistance in the platinum wire, with 
NATURE 
[ Sept. 15, 1870 
the resistance being increased fourfold by an_in- 
crease of temperature from the freezing point to about 
3,000° Fahr. The ratio of increase is, however, not 
uniform, but follows a parabolic law which the author 
embodied in a table. The pyrometer last described is 
the result of more careful investigation on the part of 
Mr. Siemens, who has been animated by a desire to fill 
up a blank in the means at our disposal to carry on 
metallurgical inquiries with a high degree of certainty, 
and he therefore does not seek any commercial compen- 
sation, through the Patent Office or otherwise, for using 
this invention. 
A discussion followed, in which Mr. Snelus, Mr. I. L. 
Bell, and Mr. E. A. Cowper took part. 
II. “On the Efficiency and Durability of Plain Cylin- 
drical Boilers.” By Mr. Jeremiah Head, Middlesborough. 
The author of this paper aimed at pointing out the many 
high qualities possessed by the plain cylindrical boiler, to 
investigate the cause and extent of the defects which 
they possess, and to point out satisfactory remedies for 
them. Such boilers are still in large request. Out of 
17,825 boilers now on the books of the various boiler 
insurance companies 4,052, or 22°7 per cent., are of this 
type. But such boilers are very liable to fracture and 
break their backs, and Mr. Head gave an explanation of 
the causes of such occurrences, and explained the method 
which he had adopted to prevent the recurrence of such 
a mishap in a boiler that had been repaired about the 
beginning of March last. His plan is to suspend the 
boiler upon volute springs. No springs are necessary for 
boilers of 30 feet long upon two supports; but for lengths 
of 60 to 75 feet five supports are required, the end ones 
being furnished with double springs. 
The discussion following this paper was so long that no 
time was left for the consideration of a paper by Mr. 
Kohn, C.E., on ‘‘ The Production of Alloys of Iron and 
Manganese, and on their Application to the Manufacture 
of Steel.” A paper on “A Contribution to the History of 
the Puddling Process” was also left over for consideration 
at the next meeting in London. On that occasion the 
place will be selected for the next autumn meeting. 
In the afternoon of Wednesday, the world-famous works 
of the Dowlais Company were visited by the members of 
the Institute. Thursday was occupied with a visit to 
Swansea, where an inspection was made of the Landore 
Steel Works, where the Siemens-Martin process is carried 
on ; the Hafod Copper Works, belonging to Mr. Vivian, 
M.P., and the Spelter Works. Friday was devoted to a 
visit to the Crumlin Viaduct and the Ebbw Vale Com- 
pany’s Iron and Steel Works. These several inspectorial 
visits were thoroughly enjoyed, and the hospitality with 
which they were attended was most profuse. Doubtless, 
many of the practical and professional men who were 
present at the inspection gained a large fund of mental 
insight which will, ere long, be applied to practical advan- 
tage, or, at all events, be put to a practical test. 
JOHN MAYER 
LETTERS TO THE EDITOR 
[Zhe Editor does not hoid himself responsible for opinions expressed 
by his Correspondents, No notice is taken gf anonymous 
communications. | 
A Mirage 
As several notices of Mirage seen in Britain during the present 
year have recently appeared in NATURE, I venture to trouble you 
with the following substance of a few brief notes (made on the 
spot) of an instance which I witnessed on April 15, 1870. 
With a companion I was walking slowly from Chesilton, in 
the ‘‘Isle” of Portland, along the western slope of the famous 
Chesil Bank, in a north-westerly direction—my friend on one of 
the numerous narrow terraces into which the slope is broken, I 
on that next below. The day was bright and warm, and the sea 
was calm. Having occasion to stoop down, I caught sight of 
what for the moment I thought a considerable pool of water on 
increase of temperature. This rise is considerable, | the terrace on I which stood, in the direction in which we were 
