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pressure obtained by a force pump, which does not aiford an 
absolutely reliable proof that the boiler has passed the ordeal 
without injury, and moreover requires a special apparatus. 
The plan which had been adopted by the Author for two 
years past, with perfect success, was free from the objections 
which applied to the above, and is as follows : The boiler is 
entirely filled with water. Then a brisk fire is made in, or 
under it. When the water has thereby been warmed a little, 
say to 70° or 90° Fahrenheit, the safety valve is loaded to the 
pressure up to which the boiler is to be tested. Bourdon’s, 
or other pressure indicator, is then constantly observed ; and if 
the pressure, occasioned by the expansion of the water, 
increases continuously up to the testing’ pressure, without 
sudden stoppage or diminution, it may be safely inferred that 
the boiler has stood it without strain or incipient rupture. 
In the trials made by the Author, the pressure rose from 
zero to 62 lbs. on the square inch in five minutes. The 
facility of proving a boiler by this method was so great that 
he trusted that owners would be induced to make those 
periodical tests, without which, fatal experience had shown 
that no boiler should be trusted. 
MICROSCOPICAL SECTION, 
November 21st, 1859. 
Messrs. J. G. Lynde and A. Brothers exhibited the 
process of photographing microscopic objects, as used by 
them, and which, from the specimens produced, appears very 
excellent. 
The first experiment was the photographing of a thin 
section of the spine of the Echinus ; a frds inch object glass 
of Messrs. Smith and Beck being used, with the focussing 
glass at a distance of three feet six inches. The object was 
illuminated with an argand gas lamp. The image being 
received on an ordinary collodion plate, and exposed for 
