578 NATURE 
ULY 22, 1915 
ohh 

been made possible by the use of more sensitive junc- 
tions to receive the radiations. The Féry pyrometer 
has been modified by Whipple for determining the 
temperature of molten metals by mounting the pyro- 
meter at the open end of a fireclay tube, so as to 
be permanently focussed on the closed end which is 
immersed in the metal. Foster uses a similar plan 
in connection with his fixed-focus pyrometer (Fig. 3) 
the end being closed by a salamander tube which js 
dipped into the metal. The telescope is pierced by a 
tube open at both ends, through which air may be 

Fic. 4.—Paul’s radiation pyrometer. 
forced with the view of preventing fumes from reach- 
ing and corroding the mirror in the event of breakage 
of the immersion tube. Mr. R. W. Paul has intro- 
duced a radiation pyrometer in which the rays are 
received in a tube containing a polished cone, a june- 
tion at the apex receiving the radiations. This type 
of instrument, originally due to Thwing, gives the 
same reading at all distances within a given limit, 
and therefore requires no focussing. A unipivot 
galvanometer is used as indicator (Fig. 4). A high 
a 
BECKER, CONDON & B'HAM: 


















Fic. 5.—Heathcoie’s extinction pyro.neter. 
degree of accuracy has now been attained with radia- 
tion pyrometers, as is proved by tests on commercial 
instruments conducted at the National Physical 
Laboratory. 
Optical 
The standard forms due to Féry, Wanner, and 
Holborn and Kurlbaum are now weil established, and 
have been improved in details with a view to indus- 
trial use. A new type of optical pyrometer, based on 
the principle of colour extinction, has been introduced. 
In the form devised by Heathcote in the Research 
NO. 2386, VOL. 95] 
Pyrometers. 
| Laboratory of the Rudge-Whitworth Company, cells 
| containing a liquid of the correct colour and density 
| are used, so that the luminous rays from the heated 
object are extinguished at a given temperature. The 
instrument consists of an eye-shade (Fig. 5) in which 
| four cells are mounted, two of which are capable of 
extinguishing the light at the 
working temperature, whilst the 
other two correspond to a slightly 
higher temperature. Either pair 
may be brought before the eyes by 
moving a slide, and when the 
heated object is just visible in the 
lower pair, but invisible in the 
higher, the correct t mperature 
has been attained. In another 
form a single cell is used, in 
which the depth of liquid may be 
adjusted until extinction occurs, 
and the temperature read off on a 
scale graduated in temperatures 
according to the depth. 
Another form of extinction pyro- 
meter has been designed’ by Alder 
and Cochrane (Patent No. 27,033, 
1913), Shown in Fig. 6. This con- 
sists of a small telescope, the rays 
through which are intercepted by 
a wedge of dark-coloured glass, 
which is moved until the sighted 
object just ceases to be “visible. 
Temperatures are read from a 
scale which moves with the prism, 
and the range may be increased 
by inserting a piece of tinted glass 
in the eyepiece, and reading from 
a second scale prepared with the 
glass in position, 
An important paper, embodying results which sug- 
gest a new type of optical pyrometer, was read by 
Paterson and Dudding before the Shy sical Society in 
March, Ig15- It was shown that the temperature of 
many metallic substances could be measured by match. 
ing the colour against that of a black body until 
identical. A  Lum- E 
mer-Brodhurt photo- 
meter was used, and 
the temperature of 
the black body varied 
until equality of hue 
was obtained. Fila- 
ment lamps, with an 
ammeter and rheo- 
stat in the circuit, 
| were thus matched, 
| and became second- 
| ary standards, a 
given current corre- 
sponding to a known 
temperature. An 
optical pyrometer on 
these lines appears 
quite feasible. 
Lovibond has sug- 
gested an optical 
pyrometer in which 
a standard source of 

meter. 


light is brought to Fic. 7.—Foster's recorder. 
equality ‘of tint 
with the heated object by interposing tintometer 
glasses. 
Recorders. 
The value of temperature records is now so much 
recognised in the industries that all makers of pyro- 


Fic. 6.—Alder and Coch- 
rane’s extinction pyro- 

