Correspondence. — 113° 
The memoir gives the details of manipulation, and provides for the 
adulterations to which the cyanid of potassium is liable. 
ides the researches which have been presented to the Academy 
of Sciences, which will soon be known in America, if not already 
there are others either unpublished or little known, which merit at least 
@ mention of their titles to engage for them the attention of the scien- 
public. 
_ Of this number, one is the apparatus of Ruhmkorff, already men- 
tioned, by means of which, dynamical electricity is transformed into 
Static electricity. Another is, 
A new Process for determining Dilatations, by M. J. F. S1npeRMAnn, 
the director, as learned as he is modest, of the National Conservatory 
of Arts and Measures. This process was employed for the first time in 
the comparison of the standard meter which formed a part of the col- 
lection of weights and measures sent to the United States by the French 
lie in exchange for the collection of weights and measures from 
the government of the United States. : 
5 The processes hitherto used give the dilatations only to a sixteenth 
- millimeter, which degree of precision had been considered very 
But M 
this process consists essentially in employing a new method for tracing 
#0 Invariable length on the rules used in investigating the dilatation 
between 0° and 100°C. To arrive at this invariable length, M. Silber- 
ten, USeS @ beam compass with very solid points held in a wooden 
trough full of melting ice. ‘This compass is made of a steel rule 1-20 
fang, 5 centimeters wide and about 8 millimeters thick: it carries two 
very solid points, attached at a distance of a meter apart. The points 
pe: 
ngs through which the points of the com 
a Whilst the compass Aes the melting cee Fae. which is under trial 
'S also put in, and this last is kept in for at least two hours. After this 
ime has elapsed, the beam compass is placed on the rule, and after the 
Polnting is done, the latter is taken from the melting ice. The rule is 
~t put in boiling water for two hours, preparatory for the second 
difference of dilatation is then determined by means of 
combination of lenses, the arrangement of which cannot be 
Well explained without ficures. | 
OM. Silbermann has had the kindness to go through this process in my 
ap cc> and it will give some idea of its simplicity when I say, that 
aferwards Tepeated the process with little trouble and very satisfac- 
lory results, 
Peg Same process has also been used to determine the co-efficient of 
the on for a meter of platinum, sent by the French government to 
Great Exhibition at London. 
United absolute dilatation of the meter of annealed steel, sent to the 
Pérats States was found to be 1-0502 millimeters, between the tem- 
tit da of 0° and 100° C. Compared with the standard of platinum, 
ted at the Conservatory of Arts and Measures, the annealed steel 
Senus, Vol. XV, No. 43.—Jan,, 1858. 15 
