When the practice of ensilaging green material for feeding animals was first introduced into the United States there was much discussion as to the construction of silos. Many advocated building them of stones, brick, or grout, though some were built of wood. As a rule, they were built either square or in the form of a parallelogram, in a few cases octagonal. Experience soon showed that the silage was preserved better in the wooden silo than in those constructed of other material. For this reason, and because the wooden silo is most cheaply constructed, wood is now in universal use for building them.
At first heavy frames were erected which were covered with two, three, and even four thicknesses of boards. Sometimes building paper was placed between the inner and outer boards. The octagon and the round silo soon supplanted those having square corners. As built, too often the walls could not be or were not fully ventilated. The thick walls remained more or less damp throughout the entire year or, if dried out when empty, lack of ventilation superinduced dry rot. Cases were not infrequent where silos were found to be practically useless without rebuilding in four or five years. Where everything was at its best, the frequent shrinking and swelling of the wood resulted finally in so destroying its elasticity that it did not return to its normal size when the silo was refilled. Since there was no means of tightening these silos the air soon entered them freely, which resulted in serious loss of fodder. By reason of the costliness and defects of stone and grout silos, and the failure in many cases of square-cornered wooden ones to preserve the material satisfactorily, and because of their perishable nature, much attention has been given to the shape and material of silos.
Fig. 130. The stave silo.
From all the evidence attainable, the conclusion is reached that the round, tall, stave silo is best. It is simple in construction, inexpensive as compared with most other kinds, and reasonably durable. The fact that it dries out fully during the summer, thereby destroying all germs of decay, coupled with the other fact that at any time it can be made tight by means of the hoops which serve to hold the staves in place, makes the round, stave silo par excellent. The staves should be two inches thick and from four to six inches wide, bevelled to suit the size of the structure. The hoops are usually of round galvanized iron one-half inch in diameter. They are placed about three feet apart, the spaces between the hoops being wider near the top than they are near the bottom. The hoops are made in sections of variable lengths; the ends of each section are furnished with lugs, that the hoop may be shortened and the silo tightened with ease. The illustration ([Fig. 130]) shows an emergency silo built of rough green hemlock plank unbevelled, hooped with “American woven wire fence.” It is 24 feet high, 12 feet in diameter, cost $35, and has a nominal capacity of 50 tons. A flat board roof serves to keep out the snow and most of the rain. It is placed in the open to test its durability. It has been in use one year, and so far it is entirely satisfactory, though the staves would be better if they had been beveled.
How long will this inexpensive silo last? That remains to be determined. Judging from other silos of similar construction which were erected several years ago, I judge it will last 15 or 20 years with slight repairs. When left thus exposed, will the silage freeze during the winter? In extremely cold weather in central New York, when the thermometer drops to 10° or 15° below zero, the material at the top will freeze. If straw be spread over the silage to the depth of a few inches, it will prevent the escape of heat and freezing. A portion of the straw covering is thrown back out of the way, the silage wanted removed, and the covering returned. Such precaution is only necessary during a few of the coldest days.
CHAPTER XX
PROTECTION FROM LIGHTNING
A flash of lightning is one of the most feared of nature’s manifestations of power; and yet by the use of proper precautions its ability to injure persons and property can be lessened greatly. Speculations as to the nature of lightning were vague until Benjamin Franklin boldly sent a kite into the teeth of a storm and tapped the accumulated electricity in the cloud to charge one of his storage jars. He connected the cloud with his jar by a wire made of a material which he knew would conduct the electrical charge, and at the same time he took the precaution not to hold the end of this wire himself. He introduced between the end of the wire and his hand a piece of silk cord, which is a non-conductor of electricity. Had he taken hold of the end of the wire, the charge would have passed through him with probably fatal results.
What is lightning? One naturally inquires for the reason of this storage of electrical energy in the clouds. The explanation is not forthcoming—at least there is none which is entirely satisfactory—but the facts are well known. The mass of water-vapor which forms the clouds becomes electrically charged just as a rubber comb does when rubbed on the hair on a dry day, or as an ebonite ruler does when rubbed on a cat-skin. Perhaps by contact with the air, which is in motion, the particles of water become charged, and by the union of multitudes of these the clouds are charged to a tremendous pressure. Lightning can be produced artificially on a small scale by means of electric machines, and the results of study of these artificial discharges have been to show the following facts: The air is not a conductor of electricity, but when the electrical pressure between two points becomes sufficiently great the electric charge jumps suddenly between the two points at which the pressure exists. It punctures a hole for itself through the air. Lightning is the result. This discharge is very violent, and it is accompanied by a strong smell of ozone, which is only very strong oxygen. If one were to examine the points of the electric machine between which the discharge took place, they might be found either hot or cold, depending upon their size and the material of which they were made. Some materials offer more resistance to the passage of the electric charge than others, and when a considerable resistance is offered, heat is produced in appreciable amounts at the places at which the resistance is met. The application of this principle will be seen when the effects of real lightning are considered.
In [Figs. 131], [132], and [133] are shown lightning flashes taken by Mr. W. N. Jennings.[9] These flashes are so soon over that without the aid of the sensitive photographic plate it would be impossible to study them. It will be noticed that the path of the charge is not straight, but quite irregular; this path being that in which there is the least resistance to the passage of the electricity. One strange phenomenon which is brought out clearly in the pictures is that the discharge very frequently divides into several branches. This is because it finds easy paths in several directions and divides into smaller discharges, thus finally disappearing.