420 ON THE CONTRACTION AND EXPANSION OF ICE. 
ice field, as circumstances may direct, a tolerably correct idea could 
thus be obtamed of the amount of expansion per degree of tem- 
perature, per foot or per mile. 
I have, however, been desirous to ascertain by actual measurement 
the exact extent of contraction and expansion of ice, not only for the 
sake of obtaining such information, but also for the purpose of veri- 
fyimg the deductions formed from general observations during previous 
winters. Circumstances prevented me from undertaking the experi-_ 
ment before the middle of January last, at which time I selected a 
mill-pond near Cobourg, in preference to Rice Lake, as the site of my 
operations. 
The pond was adjacent to my dwelling, was shallow, (thereby pre- 
serving a more uniform temperature under the ice), and, being of 
small extent, my operations were not so liable to interruptions by a 
nip or a squeeze as they would be on Rice Lake. 
As it was desirable to experiment on as large a scale as possible, I 
proceeded to cut an opening, in the thick pond ice, one hundred and 
five feet in length by ten in breadth, from which the old ice was 
hauled out and new ice permitted to form in its stead. A rough shed 
was erected over this opening to prevent the admission of snow. 
When the new ice within the shed attained a thickness of one and 
a-half inches, I reduced its dimensions to one hundred and three feet 
in length by seven in width, having it floating and perfectly isolated 
by a channel eighteen inches in width between it and the surrounding 
pond ice. ; 
Within eighteen inches of each end of this floating ice, | inserted 
vertically small blocks of: two inch pine plank, which, being frozen in, 
became firmly embedded in it. These blocks answered admirably the 
purpose of permanent fixtures, to one of which I attached and nailed 
the end of a seasoned pine or deal rod, three inches in width, one 
hundred feet in length, and one and a-quarter inches deep, and firmly 
connected at the joints. 
To the other block was firmly clamped a target, through which 
the graduated end of the rod moved freely. 
I may add that the graduated rod was an American engineer's 
levelling staff, and read accurately to the thousandth part of a foot ; 
small rollers were placed under the rod to prevent its freezing to the ice. 
This floating ice was kept perfectly isolated from the main field, 
