Classified, there are about ten distinct types of the window-pane frost. Representatives of each and all types never appear at any given time upon one window; and strangely enough the designs are never precisely alike on any two panes of glass. Reduplications of any previous design are extremely rare, and would only occur when a multitude of identical conditions occur. This is rather singular, when we consider the different factors which go to form the window-pane frost. Certain panes of glass vary in thickness and in surface topography, also in the arrangement of minute, invisible scratches, and the accumulation of dust particles which collect from day to day, all of which affect the arrangement and collection of the frost crystals. It has been observed that double windows and furnace-heated apartments are not favourable to frost formations; but in rooms which are allowed to cool off at night, and in rural dwelling houses which are not heated by steam or furnace the Frost Spirit loves to work, and decorates their windows with his choicest etchings. [Illustration: 53. An unusual design] [Illustration: 54. A powdering of small flowers] The beautiful frost studies illustrating this chapter were photographed in northern Vermont, where the winters are long and the cold very intense; affording the very best opportunities possible for the development and study of the frost etchings. These studies are, of course, somewhat magnified, yet you will have no difficulty in recognising many familiar frost designs. No. 35 is a linear type, and of rather common occurrence, easily recognisable. In No. 36 the photographer scratched his initials crudely upon the window-pane; instantly Jack Frost began to elaborate the crude work, with much better effect. No. 37 is easily suggestive of a strip of very costly hand-made lace. No. 38 is a very beautiful arrangement showing two distinct types of window-pane frost. Observe how each type never intrudes upon another. The white fern-like type is raised from the glass, and was formed in a very cold room where it slowly developed and grew for days. No. 39 is another striking arrangement of the two types; observe the very delicate fleecy patterns of the frost which forms a background for the fern-like scrolls. No. 40 shows a perfectly developed fern; while in No. 41 we have a strikingly beautiful example of a group of ferns; this type is heavily laid upon the glass, and develops in zero weather. No. 42 shows very clearly, in detail, the granular formation of the frost which has drawn away from the true frost crystals forming in detached places, in order to give them room to complete their elaborate patterns. No. 43 shows an extremely graceful feather effect, with beautifully curved scroll like tips. No. 44 is a very striking arrangement of window frost, showing exquisitely arranged branches, resembling evergreens, shooting out into the clear spaces upon the glass. [Illustration: 55. A maple leaf etching]