100 KANSAS CITY REVIEW OF SCIENCE. 
self up in the dazzling rays of the Sun. He will reach inferior conjunction with 
the Sun near midnight of the 7th; after which he will be morning star till July 
20th. 
Uranus occupies a good position for observation. It is about 5° nearly west 
of Beta in Virgo. It is just visible to the naked eye when the Moon is absent - 
like a star of sixth magnitude. Neptune is a morning star, and will be very near 
Venus June 8th. Both will be in the same field of view in a telescope; Neptune 
being about 10' south of Venus. The latter is getting nearer the Sun and dimmer, 
but is still a prominent morning star about daylight. Mars on the loth is an hour 
above Venus, but not of much prominence or interest. On the 19th Venus and 
Saturn will be in conjunction — Saturn being 35' south of Venus. 
CORRESPONDENCE. 
SCIENCE LETTER FROM PARIS. 
Paris, May 5, 1883. 
Boiler explosions are of late of frequent occurrence, and the conclusion of 
the inquiry into a catastrophe is, " cause unknown, the boiler was in a good state 
and the water at the proper level." The latter two explanations may be quite 
correct. Now the cause which escapes control is exactly what remains to be 
investigated. Professor Donny, of Ghent, in 1S46, drew attention to the fact 
that water when freed from the air which it always holds in solution, boils no 
longer at 212°, but must be over-heated to some 256° before it reaches the ebulli- 
tion stage. Then the transformation of water into steam takes place suddenly 
and in volumes, as that the vessel containing it bursts. 
Thus there is water saturated with air normally, and water which on being 
progressively heated, parts with its air. In the latter condition when the temper- 
ature is augmented, no steam is generated, the air being no longer there to aid 
the work of ebulUtion. The fireman consults the indicator and finds the water to 
be at the same level ; he concludes the temperature to be insufficient; he adds 
fuel upon fuel ; the indicator remains still stationary. Suddenly the water having 
been over-heated, to 256°, immense volumes of steam are generated suddenly 
and an explosion follows. 
The danger is at its maximum in the morning and at noon when the opera- 
tives resume work. About seven in the evening the fireman banks the fires, after 
having filled the boiler with water leaving the manometer indicating a pressure of 
four atmospheres. In the morning the pressure is down to say two atmospheres ; 
it adds fuel to augment to six atmospheres. However, during the night the boil- 
ing water has gradually got rid of its air and has become dangerous, presenting 
