, 1870-08-07
&tYuclllrr OF Ice.

y letter from correspondent Of Professor
nonney as Ottawa. Canads, published in Nd
,ure, eays:
..1he zee On our inland lal.s il generally
two or three feet thiek. As tho spring sd-
vaucts, al inch or two may bo melted away
from the lower surface. aul somo1has more
fsuu .he uplez oue, but tho thickness il not
materially reduced until its faual disappear
allce. The trst higu Of the approaching
breakup in that tho ice becomes 1rJ, from the
p1isf.attc structure haying commenced to
nloni Itself, allowing the euIfacE-nater TO per-
colate through the iutctetiecs it il then said
to le Eouey-coEbed- Ii this state the lower
layers OF transparent ice are sill solid, though
II you cut oEt block the prisna.ic structure
wLieh has been formed from ! mix-
ture OF snoW. aud wxter, readily b1eaks
up urder your feet into I:t1n granules Of ico.
Tho next stage il that tho ice becomes
black, showing tEat It il soaked, - il we're,
With water and il 1t this tlE1e there is any
oEen water, a3 whore river falls into tho
lake. and wind enough 10 cro1te swell, the
wL.1e es1face Of tie ice may DO observed 10
| uE1E!atc. Even tLcn, sometimes. I sinGle
nights frost may mako all firm again, and you
mny even trust horses upon II. II the ice now
brrals up psematu!ely with . high wiad. it be-
comes mass of spieulr Of ice which haSo not
reached the melting point, and which have
teen accumulate to the depth Of sir or se@cn
feet ssainet the edge Of the ice, which has not
yet broken up. Dut II there Is no wind, tue
whole surface Of the lake mag appear an un-
broken shect Of black ice, still couple OF feet
thick, till, in IN astonishiDclv short space Of
tine, sometimes not more tAen few ninu.es,
it disappears as If by magic. So sudden is this
disappearance that the ice isporulsr1y believed
to elnk.
II once had very good opportunity Of no.
ticiEE Ills sudden disappearance / hal built
on the ice during tho winter pier of logs
titled with stones, and wbeu the spring came,
il e.'ttie.t down 10 tie bottom, carrying with it
!; huge Gale Of the ice. When the lake lad
vI'tEt1. l went round the pier IN my canoe to
rec II il had settled evenly. There At the bot.
Il m, in rix or seven feet OF water, lay the
ake CT ice 1t had carried down, Will the chps
I'll! I'uls,l'led il it which We had ms1e in IN
b1ai.ilpg the pier: and. aa looked, blocks
wn,:sd 1reaE Oft Of foot or more in thick
lts, rise 10 tho surface, break up into spi.
ci..a aid almost instautAueous1y disappear.
Il quite agree with you that these prisms
have no connection with the he1A,onal form
| Of ice crystalr, Lut doubt your explanation
that they atise {run the contraction Of the
ice At il approaches the melting point. Does
| ice contract under snch circumstances: Al
I though wafer expands 10 freezing, and rlc.
| rfrs0. cccupies 1ees bulk when feconvsrtol
into water. yet. as long IA il remains ice,
rauds with heal, Ike other substances, It Ii
certain that. after nights h11d frost. sur
| f1ce Of glare ice will bo covered with
multitude Of srnau cracks from the
contraction: md larger cracks vii
so1reti1 extend through tlas whole
thickness. with report Altnost Ike that OF 1
cannon. knew = case OF railway bridge
built on piles over shallow lake, which VA.
entirely destroyed by the alternate expansion
and contraction Of tho ice With variations o.
temperature. With \ spell Of COLI the ic,
would be split up With iunutnerahle cracks
into which the water iusinnAted itself an.
f1ozc. With warmer weather the whole eI
banded. showing the ice up On the shores. o.
fresh contraction, the ice could not be with
drawn froso The shores. bnt cracked agli,
in preference. The consequence was, tha
Of the lake toward 10th shores. The piles il
the middle remained upright. but the ueAte
they were to each shore the mere they wer'
driven ont OF TIE perrendicular+ The datn2s
was great the arst winter, but it WAS repaired
The next winter, By Cutting mp the ice With ic,
| BLOWS, and hy mskng ctubankmsnts from csc!
shore, the damage vas sought to be arrested
bridge had to Re altogether abandoned, a.
while The piles in the middle t
still upright, thoee near each shore II
now laid Almost fat. It Is to this constau
motion in one direction, ar;sing from slternat
expansions and coptractions. thxt ! have =
l wsys in great measure attributed the doW1
w1rd progress OF G3suerH.
A. TIE true explanation Of the pris1ati
structure appears to me to be the lines Of d
tnl'hles which rou yourself notice. Tnes
arc visible IN ice before any thaw hAs con
| 1otnced, and in the process Of freezing th<
| seeu to be formed in vertical lines Nhe
The thAw oceurs, these lines Of bubbles for
| the centres, ~ it were, from which it pen
trases in every direchon through the nsss-