Society of Sciences of Haarlem. 147 
tirely on the weight P attached to the centre of the square 
plane. 
In the 18th vol. of the Memoirs of the Academy of Petersburgh, 
Euler has treated this subject in all its generality with admirable 
skill and profoundness (De pressione ponderis in planum cui 
incumbit) ; but in the judgement of d’Alembert (Opusc. Mathem. 
tome viii. p. 40, § 13) the solution is still uncertain and hy- 
pothetical ; and, in fact, the principle upon which it is founded 
seems rather to be a mathematical hypothesis than a physical 
principle. 
It is therefore required, : 
First. That this principle be discussed fundamentally, and 
that it be demonstrated in a positive manner, whether it is or is 
not admissible as a physical principle. ; 
Second. In the event of the demonstration being in the nega- 
tive, that it be examined, whether by presenting this principle 
in any other point of view it cannot be confirmed, and the beau- 
tiful theory which flows from it be thereby preserved. 
Third. \f neither of these trials are satisfactory, that there be 
assigned for the particular case which has been specified above, 
4 principle which shall be free from all objection. 
2. Assuming that there is an identity between the forces which 
produce electrical, and those which produce galvanic phzno- 
mena; whence comes it that we do not finda perfect accordance 
between the first and the last ? | 
3. Many modern authors believe in the identity of chemical 
and galvanic forces :—Can the truth or falsity of this opinion be 
proved ? ; 
The prize offered for each of these questions is a gold medal 
of the weight of twenty-five ducats. The memoirs may be writ- 
ten in Latin, French, Dutch, or Flemish, and transmitted pre- 
vious to the Ist of February 1819 to the Secretary of the Aca- 
demy M. Van Hulthem. 
SOCIETY OF SCIENCES OF HAARLEM. 
‘The following questions in the Physical Sciences have been 
or dee by this Society for competition previous to the Ist of 
anuary 1519: 
1, What is the origin of carbon in plants? Is it produced by 
the vegetation itself either entirely cr in part, as the experiments 
of M. Vou Crell appear to have established, and as many philo- 
sophers suppose? — If it is so, in what manner is this production 
effected? {f not, in what manner does the absorption of carbon by 
plants take place? Is it effected after it is combined with oxygen 
and transformed into carbonic acid, or in what other mode ‘. : 
K 2 . To 
