Serre = 
a 
On the Dry Rot. 169 
such delicacy as to revolve by the earth’s magnetism. Placed 
upon the top board of the machine, the connexions being made, 
it revolves rapidly by the attractions and repulsions of the upper 
poles of the large magnets underneath. 
A small electro-magnet, charged by the three inner coils of one 
of the armatures, sustained permanently ten pounds, while the 
machine was in action. 
Fusion of iron filings.—When a wire from one pole of the 
machine was placed in a heap of fine iron filings, and a bunch of 
these raised by a magnetic bar connected with the other pole, 
the connecting shreds of filings, sometimes an inch in length, be- 
came intensely ignited throughout, fused into a mass and fell off, 
leaving frequently a globule attached to one of the poles, which 
glowed for a time after the contact was broken, and then ex- 
ploded, as is seen with particles of iron burning in oxygen. This 
curious experiment succeeds best, when the filings are held be- 
tween two opposite poles of magnetic bars, connected each with 
the poles of the battery. 
Art. XV.—On the Dry Rot; by Putnenas Rainey. 
Middletown, (Conn.) March 22d, 1838. 
TO PROF. SILLIMAN, 
Sir—Permit me through the medium of your very valuable 
and widely circulating Journal, to lay before the public the fol- 
lowing facts and observations in relation to the dry rot in timber. 
It is matter of history, that the timber of the ancients lasted 
some hundreds of years longer than that of the moderns, and 
there is no record that their timber was subjected to a 
process to make it durable. It is therefore probable, the 
why the dry rot exists to such an alarming extent in the _— 
wood of the timber of the present day, is to be found in the sea- 
son of cutting the trees. It is probable that the present general 
practice of cutting timber in the winter was avoided by the an- 
cients, and that it originated in England, when the botanical 
theory, sy sshipen a pling mai amaaae ium the 
year, was first promulgated. 
Vout. XXXIV.—No. 1. 22 
