[…] It is moſt remarkable on the ſurface of ſnovv, vvhen covered vvith hoarfroſt, and on other bodies vvhere hoarfroſt moſt abounds. In ſuch caſes, I have often found the ſurface to be ſeven degrees colder than the air at the diſtance of tvvo feet; […]

I was informed that the clear spots which are surrounded by woods, are particularly liable to hoar frosts in the spring and autumn; […] When any of our parties pitched their tents near the exits of rivers, they found the nights colder, and observed hoar frosts to occur more frequently, than those whose encampments were differently situated.

The mean temperature of the day and night at which injurious hoar-frosts may occur, may, relatively to the freezing-point, be very high.

In the mornings hoar[-]frost lay thick upon the ground, and thin ice formed in currentless shallows and overlay the muskrat runways.

Aristotle deals with many of these cosmic matters in Meteorology, along with the Aurora Borealis, comets, the Milky Way, rain, clouds, dew and hoar frost, snow, hail, winds, rivers, springs, climate, coastal change, where does the sea come from and why is it salty, more on winds, earthquakes, volcanoes, thunder and lightning, hurricanes, haloes and rainbows.

On Sunday night, January 23, ſeveral things vvere laid out at the Obſervatory, ſuch as ſheets of brovvn paper, pieces of boards, plates of metal, glaſſes of ſeveral kinds, &c. vvhich all began to contract hoar-froſt ſeemingly as ſoon as each body had time to cool dovvn to the temperature of the air. The ſheets of brovvn paper being ſo thin acquired it ſooneſt, and vvhen beheld in candle-light they became beautifully ſpangled over by innumerable reflections from the ſmall cryſtals of hoar-froſt vvhich had parted from the air.

This striking fact, of the lower temperature of the surface on which dew and hoarfrost are forming, it was always found difficult to explain; for the transition of a body from the state of vapour to the fluid or solid form is always accompanied with an evolution of heat, […] The surface is not warmer in consequence of the formation of the dew or hoarfrost, but the dew or hoarfrost is deposited because the surface is previously cold; and its low temperature, compared with that of the air above, is owing to the discharge of heat by radiation.

Hoar frost forms when water vapor sublimates onto a surface. It is the frozen equivalent of dew. […] Conditions leading to hoar frost formation include the movement of vapor within the snowpack, the presence of supersaturated air in crevasses, ice caves, and animal burrows, and the occurrence of clear evenings with high levels of outgoing longwave radiation.

However, high mountains with a long winter and long dry spells, hoarfrosts and infertile soils are not an ideal environment for some annual crops but are well suited for perennial industrial crops and forest species.

The samples of hoar frost collected at all the stations contained few NO₃⁻ ions; this may have been because frost forms at night, when the intensity of road traffic is 2–3 times less than during the day. The largest proportion of NO₃⁻ ions was found in the farmland samples of hoar frost; the reason for this may be the application of nitrogen fertilizers in agriculture.

Hoar frost

Meaning

Noun

Synonyms