114 Chronicles of Science. | Jan., 
The subject of the transparency of red- or white-hot metals was 
referred to in our last Chronicles. It is generally believed amongst 
scientific men that the supposed phenomenon is merely an optical 
delusion. A correspondent of the ‘Chemical News’ has, however, 
adduced an observation on the opposite side. He says a few weeks 
ago he went over some steel works in the North of England, and 
there the manager spoke of it as a well-known fact that steel at a 
white heat was transparent. In proof of this he showed that when 
the molten metal was being poured out, the edge of the crucible 
appeared to be distinctly visible through the molten metal. This 
could only be seen directly the crucible was taken out of the furnace 
before it had cooled in the least. 
Mr. A. E. Fletcher, Government Inspector of Alkali Works for 
the Western District, has constructed a most useful instrument for 
measuring the velocity of a current of air. He uses it for measuring 
the speed of air in flues and chimneys. The construction of the 
apparatus is based on the fact that a current of air, passing across 
the open end of a straight tube, causes a partial vacuum init. An 
application of this principle is seen in a small toy in common use, 
in which a liquid is made to ascend seyeral inches ina vertical tube, 
by blowing through another tube across its open end ; it rises by 
virtue of the partial vacuum caused by the current of air which 
crosses it. If then a straight tube is inserted through a hole in the 
brickwork of a chimney or flue, so that the current of air in the 
flue passes across its open end, a ‘partial vacuum will be formed in 
it, greater or less in proportion to the velocity of the current. A 
tube in such a position will, however, communicate a suction arising 
from that of the chimney itself, besides that suction produced by 
the current of air passing across its open end, and for the present 
purpose these two must be distinguished. To effect this, two tubes 
should be inserted in the chimney, one of them having a straight, 
and the other a bent end, the bend to be turned so as to meet the 
current of air; both tubes are open. In each of these tubes will 
be experienced the partial vacuum due to the suction of the chimney 
itself. In the straight tube, however, this will be increased by the 
suction caused by the passage of the current of air across its open 
end, while in the case of the bent tube this will be diminished by 
the pressure caused by the current of air blowing into it. The 
difference therefore between the suction in the two tubes will be due 
to the action of the current of air in the chimney, and it remains 
only to measure this difference in order to measure the velocity of 
the current itself. After many trials, Mr. Fletcher adopted the 
following plan for measuring this suction. The tubes were con- 
nected with a U-Tube, and means were adopted for accurately 
seeing and measuring its slightest indications. In the first place, 
the limits were increased until they were no longer small tubes of 
