504 Prof. Challis on Theoretical Physics. 
of the trimetric system. Its composition is Os Cy, 2Ba Cy +6HO, 
and it is isomorphous with ferrocyanide of barium. 
Tridiocyanide of Barium, Ix? Cy*, 3Ba Cy + 18HO.—This salt 
was obtained in the process of separating the platinum metals. 
It forms well-defined crystals of the trimetric system. When 
treated with a proper quantity of sulphuric acid and the mass 
exhausted with ether, the iridiocyanide of hydrogen or zridto- 
cyanic acid, Ir? Cy?, 3KCy, is obtained in crystalline crusts on 
evaporating the etherial solution. It is strongly acid, and its 
solution decomposes carbonates. Crystallized from ether it is 
anhydrous. he iridiocyanide of potassium, Ir? Cy®, 3KCy, has 
been already described by Wohler and by Booth. According to 
Martius, the iridiocyanide of barium, which is easily obtained pure, 
affords a convenient means of preparing it. 
— Rhodiocyanide of Potassium, Rh? Cy?, 3 K Cy.—This salt is ana- 
logous in composition and mode of preparation to the preceding 
salt, but is acted upon by acetic acid, which is not the case with 
the iridium salt. When treated with acetic acid, hydrocyanic 
acid is disengaged and a red powder is precipitated, which is the 
eyanide of rhodium, Rh? Cy®. This deportment furnishes a means 
of separating the two metals. 
Martius further remarks upon the preparation of the platino- 
cyanides of potassium, and describes some new double cyanides. 
LXXIII. On Theoretical Physics. 
By Professor CHaruis, /.R.S., F.R.A.S.* 
| HAVE been induced to make the following remarks chiefly 
because I am unwilling to appear inattentive to the repeated 
notices which Mr. Glennie has taken of my mathematical theory 
of the physical forces. But I have occasion to do little more 
than give my reasons for concluding that nothing which Mr. 
Glennie has urged calls for a reply. Of course I do not object 
to my hypotheses being tested and scrutinized in all possible ways 
that are legitimate: at the same time I must maintain the New- 
tonian doctrine, that no arguments can be adduced either for or 
against a hypothesis which are not drawn from experience, or 
from a comparison of the mathematical results of the hypothesis 
with experience. Also it is a necessary condition of a hypo- 
thesis that it be expressed in terms which experience makes in- 
telligible. Myr, Glennie has not said that the statement of my 
hypotheses does not fulfil this condition ; neither has he adduced 
any facts contradictory to results mathematically deduced from 
* Communicated by the Author. 
