A Field Guide to Hummingbirds of North America by Sheri Williamson

By Sheri Williamson

Это наиболее детальный определитель колибри, характеризующий 31 североамериканский вид и снабженный 250 цветными фотографиями и 33 картами. Во вводной главе изложена естественная история колибри, способы их привлечения и кормления, а также места в США и Канаде, наиболее удобные для наблюдения колибри. На 31 цветной вкладке приведены иллюстрации 28 видов, 7 гибридных комбинаций, three формы альбиносов и four вида бабочек-бражников, часто принимаемых за колибри. Описание видов включает информацию о песнях и сигналах, шорохе крыльев, сходных видах, поведении, местообитаниях, распространении, систематике, охранном статусе. Для некоторых распространенных мигрирующих видов приведены даты ожидаемого весеннего прилета.
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CHAPTER V. THE RIFLE AND HOW TO CHOOSE IT AND HOW TO USE IT. Difficulty generally experienced in selecting a rifle. Consideration whether for target practice or for hunting. Condemnation of rest firing. Peck’s opinion. Practice made from a rest. Telescopes. Lieut. Godfrey’s feat. The “twist” again. A good kind of rifle. Frank Forrester’s choice. What Seth Green shoots with. A capital rifle. Gordon Cumming’s rifle. Breech-loaders must ere long entirely supersede the muzzle-loader. The best kind.

In order to find the initial velocity of rotation of a bullet, divide the initial velocity in feet by the number of feet in which one complete turn is made by the bullet; thus, the initial velocity of the Enfield rifle being twelve hundred sixty-five and one-tenth feet per second, and the turn one in six and a half feet, the initial velocity of rotation of the bullet, fired from the Enfield, is one hundred ninety-four and six-tenths revolutions per second. The greater the initial velocity, the greater the initial velocity of rotation from the same rifle, and vice versa; therefore, projectiles fired from two rifles similar in all respects, with the exception of their spirality, may be impelled with the same initial velocity of rotation, the initial velocity of the rifle with the greatest spiral being reduced; so that Friction is a retarding force, arising from the parts of one body rubbing against the parts of another.

The line of fire, with a properly fitting bullet, is constantly above the trajectory, and is a tangent to the latter toward the muzzle. Fig. 1 is a representation of a detachment, the leading part of which is marching uninjured under fire, which, owing to the elevation of the trajectory, is taking effect further in the rear. Fig. 2. The line AD indicates the axis of the rifle; AC the line of sight; and AB the trajectory or path described by the bullet. EF is a horizontal line, on which the shooter is supposed to be standing.

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