Below zero. ice forming/ Open places on the river.between Carlisle Bridge and Nut Meadow Brook

December 29

A very cold morning, — about -15° at 8 a. m. at our door. 

I went to the river immediately after sunrise. I could [see] a little greenness in the ice, and also a little rose-color from the snow, but far less than before the sun set. Do both these phenomena require a gross atmosphere? Apparently the ice is greenest when the sun is twenty or thirty minutes above the horizon. 

From the smooth open place behind Cheney's a great deal of vapor was rising to the height of a dozen feet or more, as from a boiling kettle. This, then, is a phenomenon of quite cold weather. I did not notice it yesterday afternoon. These open places are a sort of breathing-holes of the river. 

When I look toward the sun, now that they are smooth, they are hardly to be distinguished from the ice. Just as cold weather reveals the breath of a man, still greater cold reveals the breath of, i. e. warm, moist air over, the river. 

I collect this morning the little shining black seeds of the amaranth, raised above the snow in its solid or dense spike. 

P. M. — To Ball's Hill, skating. 

Walked back, measuring the river and ice by pacing. The first open place in the main stream in Concord, or no doubt this side Carlisle Bridge, coming up stream, were: — 

• 1st, Holt Ford, 10 rods by 1 (extreme width). 
• 2d, east side Holt Bend, near last, 8 by 1 1/2. 
• 3d, west side Holt Bend (midway), 3 by 1/2. (On the 28th it must have been open nearly all round to Holt Bend.) 
• 4th, Barrett's Bar, 42 rods by 6 at west end, where it reaches 12 rods above ford; extends down the north side very narrow to the rock and only little way down the south side; can walk in middle half-way. 
• 5th, a bar above Monument, 10 by 3. 
• 6th, from Hunt's Bridge to Island, or say 54 rods by 4. 
• 7th, from 8 below willow-row to 5 below boat's place, or 80+ rods by 3. 

This as far as I looked to-day, but no doubt the next was : — 

• 8th, just above ash tree, probably three or four rods long. 
• 10th, Clamshell Bend. 
• 11th, below Nut Meadow, probably two or three rods long.
• 
  

This is the last in Concord. (I do not include the small openings which are to be found now at bridges.) [Feb. 15, 1860, when the river was much more open than Dec. 29, 1859, it was scarcely open at the narrowest place above Bound Rock, only puffed up in the channel, and the first decided opening was at Rice's Bend; all below Bound Rock to Fair Haven Pond, etc., was quite solid. Hence the statements above are true.]

The longest opening is that below my boat's place; next, at junction next Barrett's Bar; next, either Clamshell or Hubbard's Bath. But for area of water that below the junction is considerably the largest of all.

When I went to walk it was about 10° above zero, and when I returned, 1°. I did not notice any vapor rising from the open places, as I did in the morning, when it was -16° and also  -6°. Therefore the cold must be between +1° and -6° in order that vapor may rise from these places. 

It takes a greater degree of cold to show the breath of the river than that of man. 

Apparently, the river is not enough warmer than the air to permit of its rising into it, i. e., evaporating, unless the air is of a very low temperature. When the air is say four or five degrees below, the water being + 32°, then there is a visible evaporation.

Is there the same difference, or some 40°, between the heat of the human breath and that air in which the moisture in the breath becomes visible in vapor? This has to do with the dew-point. Next, what makes the water of those open places thus warm ? and is it any warmer than elsewhere? 

There is considerable heat reflected from a sandy bottom where the water is shallow, and at these places it is always sandy and shallow, but I doubt if this actually makes the water warmer, though it may melt the more opaque ice which absorbs it. 

The fact that Holt Bend, which is deep, is late to freeze, being narrow, seems to prove it to be the swiftness of the water and not reflected heat that prevents freezing. The water is apparently kept warm under the ice and down next to the unfrozen earth, and by a myriad springs from within the bowels of the earth. 

I notice that, on the thin black ice lately formed on these open places, the breath of the water has made its way up through and is frozen into a myriad of little rosettes, which nearly cover its surface and make it white as with snow. You see the same on pretty thick ice. This occurs whenever the weather is coldest in the night or very early in the morning. 

Also, where these open places have lately closed, the ice for long distances over the thread of the river will often be heaved up roofwise a foot or more high and a rod wide, apparently pushed up by the heat of this breath beneath. 

As I come home, I observe much thin ice, just formed as it grows colder, drifting in gauze-like masses down these open places, just as I used to see it coming down the open river when it began to freeze. In this case it is not ice which formed last night, but which is even now forming. 

The musquash make a good deal of use of these open spaces. I have seen one four times in three several places this winter, or within three weeks. They improve all the open water they can get. They occasionally leave their clamshells upon the edges of them  now. 

This is all the water to reflect the sky now, whether amber or purple.I sometimes see the musquash dive in the midst of such a placid purple lake. 

Where the channel is broad the water is more sluggish and the ice accordingly thick, or it will answer just as well if the channel is deep, i. e., if its capacity is the same, though it be very narrow. The ice will be firm there too, e. g. at Ash Tree Rock (though it was lately open off the willows eight or ten rods above, being less deep and narrower); and even at the deeper hole next below the opening is not where it is deep, though very narrow, but half a dozen rods below, where it is much wider. 

To-night I notice the rose-color in the snow and the green in the ice at the same time, having been looking out for them. 

The clouds were very remarkable this cold afternoon, about twenty minutes before sunset, consisting of very long and narrow white clouds converging in the horizon (melon-rind-wise) both in the west and east. They looked like the skeletons and backbones of celestial sloths, being pointed at each end, or even like porcupine quills or ivory darts sharp at each end. So long and slender, but pronounced, with a manifest backbone and marrow. It looked as if invisible giants were darting them from all parts of the sky at the setting sun. These were long darts indeed. 

Well underneath was an almost invisible rippled vapor whose grain was exactly at right angles with the former, all over the sky, yet it was so delicate that it did not prevent your seeing the former at all. Its filmy arrows all pointed athwart the others. I know that in fact those slender white cloud sloths were nearly parallel across the sky, but how much handsomer are the clouds because the sky is made to appear concave to us! How much more beautiful an arrangement of the clouds than parallel lines!

 At length those white arrows and bows, slender and sharp as they were, gathering toward a point in the west horizon, looked like flames even, forked and darting flames of ivory-white, and low in the west there was a piece of rainbow but little longer than it was broad. 

Taking the river in Concord in its present condition, it is, with one exception, only the shallowest places that are open. Suppose there were a dozen places open a few days ago, if it has grown much colder since, the deepest of them will be frozen over; and the shallowest place in all in Concord is the latest of all to freeze, e. g. at the junction. So, if you get into the river at this season, it is most likely to be at the shallowest places, they being either open or most thinly frozen over. That is one consolation for you.

 The exception is on the west side of the Holt (and the depth is one side from the opening), but that is on account of the narrowness of the river there. Indeed, the whole of Holt Bend is slow to freeze over, on account of the great narrowness and consequent swiftness of the stream there; but the two narrowest points of it are among the first to freeze over, because they are much the deepest, the rush of waters being either below or above them, where it is much shallower, though broader. 

To be safe a river should be straight and deep, or of nearly uniform depth. I do not remember any particular swiftness in the current above the railroad ash tree, where there is still an opening (seen December 30th), and it may be owing to the very copious springs in the high bank for twenty rods. There is not elsewhere so long a high and springy bank bounding immediately on the river in the town. To be sure, it is not deep.

H. D. Thoreau, Journal, December 29, 1859

Immediately after sunrise . . . a little greenness in the ice, and also a little rose-color from the snow. . .. Apparently the ice is greenest when the sun is twenty or thirty minutes above the horizon. January 7, 1856 ("Returning, just before sunset, the few little patches of ice look green as I go from the sun (which is in clouds). It is probably a constant phenomenon in cold weather when the ground is covered with snow and the sun is low, morning or evening, and you are looking from it."); December 25, 1858 (“The sun getting low now, say at 3.30, I see the ice green, southeast.”); January 20, 1859 ("The green of the ice and water begins to be visible about half an hour before sunset."); February 12, 1860 ("Returning just before sunset, I see the ice beginning to be green...");
Open places in the main stream in Concord. See also  December 28, 1859 ("The open places in the river yesterday between Lee's Bridge and Carlisle Bridge");

On the thin black ice lately formed on these open places, the breath of the water has made its way up through and is frozen into a myriad of little rosettes. See December 21, 1854 ("What C. calls ice-rosettes, i.e. those small pinches of crystallized snow, . . .I think it is a sort of hoar frost on the ice. It was all done last night, for we see them thickly clustered about our skate-tracks on the river, where it was quite bare yesterday"); January 7, 1856 ("It is completely frozen at the Hubbard’s Bath bend now, — a small strip of dark ice, thickly sprinkled with those rosettes of crystals, two or three inches in diameter");  February 13, 1859 ("Ice which froze yesterday and last night is thickly and evenly strewn with fibrous frost crystals . . . sometimes arranged like a star or rosette, one for every inch or two; . . . I think that this is the vapor from the water which found its way up through the ice and froze in the night"). Compare January 1, 1856 ("On the ice at Walden are very beautiful great leaf crystals in great profusion . . .like a loose web of small white feathers springing from a tuft of down")

The cold must be between +1° and -6° in order that vapor may rise from these places.  See January 10, 1859 ("Four or five below at 3 P. M., — I see, as I go round the Island, much vapor blowing from a bare space in the river just below,")

It takes a greater degree of cold to show the breath of the river than that of man. See December 27, 1859 ("Grows cold in the evening, so that our breaths condense and freeze on the windows.")

To-night I notice the rose-color in the snow and the green in the ice at the same time, having been looking out for them. See January 10, 1859 ("This is one of the phenomena of the winter sunset, this distinct pink light reflected from the brows of snow-clad hills on one side of you as you are facing the sun."); January 19, 1859 ("I see a rosy tinge like dust on the snow when I look directly toward the setting sun, but very little on the hills. Methinks this pink on snow (as well as blue shadows) requires a clear, cold evening."); Janusry 20, 1859 ("The green of the ice and water begins to be visible about half an hour before sunset. Is it produced by the reflected blue of the sky mingling with the yellow or pink of the setting sun?"); January 23, 1859 ("I notice on the ice where it slopes up eastward a little, a distinct rosy light (or pink) reflected from it generally, half an hour before sunset. This is a colder evening than of late, and there is so much the more of it."). See also notes to January 31, 1859 ("Pink light reflected from the low, flat snowy surfaces amid the ice on the meadows, just before sunset, is a constant phenomenon these clear winter days. , , , Perhaps the green seen at the same time in ice and water is produced by the general yellow or amber light of this hour, mingled with the blue of the reflected sky.")

The clouds were very remarkable this cold afternoon, about twenty minutes before sunset, consisting of very long and narrow white clouds converging in the horizon (melon-rind-wise) both in the west and east. See December 21, 1851 ("To-night, as so many nights within the year, the clouds arrange themselves in the east at sunset in long converging bars, according to the simple tactics of the sky. It is the melon-rind jig . . .converging bars inclose the day at each end as within a melon rind, and the morning and evening are one day"); February 19, 1852 ("Considering the melon-rind arrangement of the clouds, by an ocular illusion the bars appearing to approach each other in the east and west horizons, I am prompted to ask whether the melons will not be found to be in this direction oftenest")

To be safe a river should be straight and deep, or of nearly uniform depth. See December 30, 1855  ("I perceive that the cold respects the same places every winter. In the dark, or after a heavy snow, I know well where to cross the river most safely. Where the river is most like a lake, broad with a deep and muddy bottom, there it freezes first and thickest.")