Gleanings. 429 
which at first sight would appear an objection, it is far less than 
one formed of slate, and does not much exceed one of copper. 
The iron plates-weigh three and an half pounds per square foot, 
A slate roof would cost about eight cents per square foot, but for 
durability and the ease with which it can be put on and made 
water-tight, the iron roofing would appear to be far preferable. 
The plates exhibited were cast at Troy, N. Y., and are of the 
very best quality. The patent for the eastern states is now owned 
by Mr. Hiram Hemmestone, of Troy, in which neighborhood the 
adaptation of such a durable material for roofing is rapidly at- 
tracting public attention there. Starbuck's machine shop and 
foundry at Troy has been covered on this plan, and it has also 
been adopted for the roofing of an arsenal at West Point. 
Corn Mills of the Shetland Islands. — " We Whd this day an 
opportunity of inspecting one of the primitive mills of Scotland. 
The grinding stones, usually formed of micaceous schist, are 
placed upon a frame work and beneath a roof. A strong iron 
spindle is wedged into the upper stone, and, passing through a 
hole in the centre of the lower one, is firmly fixed into the upper 
end of a strong wooden post, at the base of which are mortices 
in a slanting; direction, a number of flat boards formino; the cogs 
of a kind of horizontal w^heel. A trough from a natural rill of 
water is made to convey the motive power upon the wheel, which 
turns the upper mill-stone slowly round, and so grinds the grain, 
supplied either by an old straw basket, or other rustic hoppei*, or 
more patiently by human hands. — Wilson^ s Coast of Scotland. 
Glass Spring. — It is difficult to foresee to what perfection the 
manufacture of glass majfc be brought, and to what purposes the 
article may yet be applied. The balance spring of a chronometer 
is now made of glass, as a substitute for steel, and possesses a 
greater degree of elasticity and a greater power of resisting the 
alternations of heat and cold. A chronometer with a glass spring 
was sent to the N^rth Sea, and exposed to a competition with 
nine other chronometers, and the result of the experiment was a 
report in favor of the chronometer with the glass spring. 
Glass Milk Pans are coming more and more into use in Europe. 
Their advantages on the score of cleanliness must be obvious. 
It were to be wished that societies or institutes would appoint a 
standing committee, and put aside a small portion of their ample 
funds for the instant importation of sample articles invented 
abroad, connected with agricultural and rural economy. Truejt 
is, that in general, this may be left to the vigilance and rivalry of 
tradesmen and manufacturers; but many years may elapse bclbre 
we get the benefit of many things which might at once be profit- 
