Part 23

What Happens When We Laugh?

Laughter is what we call a reflex action. When something occurs to make us laugh, whether it is something we see, or feel, or hear, it is because certain sensory nerves receive an impression in one of three ways, carry it to the nerve centre and the nerve centre then sends the same impression along certain efferent nerves, which connect with certain muscles or glands, and excite them to activity. The action is practically the same as when you hold a light before a mirror. The rays from the light strike the surface of the mirror and are reflected back from the surface, lighting perhaps corners of the room, which the direct rays from the light could not reach, all depending upon the angle of reflection. Light will always reflect from a mirror that is exposed to it.

Now, then, when you see, hear or feel anything that makes you laugh, the sensory nerves have only to receive the impression to bring on the explosion of laughter. Something touched the laugh nerves or the laugh trigger that caused it to go off. You can prove that it is a matter of impression entirely by noting that some people can listen to a perfectly funny story, even when told by a clever performer, and never crack a smile, while others burst into uncontrollable laughter, and he who does not even smile may be listening even more intently than the other--he may even be looking for a laugh. It all depends upon the impression that is made upon the nerves. The muscles have the power to express the state of gladness which is indicated by laughter when certain impressions pass along the nerves which operate them, just as they can be made to do other things when the proper cause for action is shown them.

Why Do We Cry When Hurt?

We cry when we are hurt for the same reason that we laugh when we are glad. The muscles and nerves, under the direction of the brain, produce the cry just as the muscles and nerves produce laughter, although they are probably, but not necessarily, a different set of muscles and nerves.

When we are hurt in any part of our body or feelings the impression does not affect us until it reaches the brain. Then instantly, of course, the body and brain go to work to destroy the pain. The first thing, of course, is to give a warning to other parts of the body that there is a hurt, and our crying is a warning to other people that we are hurt. That is probably the only good that crying does. It does not remove the hurt--it only tells others of our troubles. We cry with the lower part of the brain--the only portion of the brain which is active in a little baby. This is why even a tiny baby can cry. Crying is the only thing a baby can do to give warning of its distress or discomfort. Later in life the upper part of the brain develops. This is the master of the lower part. Therefore, we do not always cry when hurt as we grow older, because the master brain sometimes tells the lower brain that to cry will not help matters in the least, even though we are inclined to cry. Sometimes the hurt or shock to older people is so great or sudden that we cry out before the controlling part of the brain has had time to get in its work of preventing the outcry, but we are able to stop crying when the master brain again secures control.

Where Do Tears Come From?

Tears are not made only when we cry. They seem to come only when you cry, because it is then that they spill over. A little part of you is making tears all the time, and your eyes are constantly washing themselves in them. You have often noticed how you wink every few seconds? You have often tried to keep from winking--to see how long you could keep from winking. Boys and girls often do that, and when you keep from winking what seems a long time, you notice how your eyes ache and feel very dry just before you have to let them wink, in spite of how hard you try not to, and just when you think you are not going to. I will tell you just what winking does for the eyes. All of the time your eyes are open the front, or the part you see things with, is exposed to the dust and dirt that fills the air at all times, although we cannot always see the dust. The wind, too, is constantly making them dry. But have you ever noticed that although you never wash the inside of the front of the eye, or pupil, it is always clean? Well, it is because your eye washes itself every time you wink. I will tell you how this is done. Up above each eye, inside, of course, there is a little gland called the tear-gland. This gland is busy all the time you are awake making tears. As soon as the front of your eye becomes dry, or if a particle of dust or anything else strikes it, the nerves you have there tell the brain, and almost at once the eyelid comes down with a tear inside of it, and so washes the front of your eye clean again. It does its work perfectly and as often as necessary. There is always a tear ready to be used in this way.

Where Do the Tears Go?

Let me show you. Look right down here at the inner corner of my eyelid, where you will see a little hole. That is where the tears get out of the eye, when they have washed your eyeball clean. Where do they go then? Did you ever notice how soon after you cry you have to blow your nose? The reason for that is that when the tears go through the little hole they run down into the nose. This making of tears and winking goes on all the time while you are awake, and after they wash your eye off they go on out through this little hole. But when you cry you make more tears come than you need, so many, in fact, that they cannot all get away through this little hole, and as there is no place else for them to go, and as there is no place to keep them inside the eye, they simply spill themselves right over the edge of your lower eyelid and run down your cheek.

Story in a Barrel of Cement

What Is Cement?

The dictionary tells us that cement is “any adhesive substance which makes two bodies cohere.” Thus any material performing this function may be called cement, such, for example, as the cement used in mending broken china. Glue also is a form of cement. This story has to do with Portland cement, which is a structural or building material used in countless ways.

Why Is Cement Called Portland Cement?

After being wet with water it hardens into stone, and it was given the name “Portland” because, when first manufactured in England, and mixed with sand and stone, it resembled a celebrated building stone called Portland, which was obtained from the Isle of Portland. Compared with other American industries, the manufacture of Portland cement is of recent origin. Formerly all Portland cement was brought from foreign countries. After successful manufacture became established in this country, however, the industry advanced with great rapidity. A few years ago the entire United States did not use as much cement as is now used in any one of our large cities. At the time these facts were written (1914) the manufacturers were making more than 90 millions of barrels a year.

What Is Cement Made Of?

Portland cement is composed chiefly of lime, alumina and silica. It is manufactured from rocks, marl, clay and shale containing these ingredients. If any one of them is lacking in the raw material as it is taken from the earth, it is supplied during process of manufacture. The greatest cement district in America is in Pennsylvania, and is known as the “Lehigh District.” A rock containing proper constituents for making Portland cement was found there in vast quantities, and for a number of years the Lehigh District was the center of the industry. In time it was found that certain clays, marls and shale could also be manufactured into Portland cement, and thus mills have been erected in all sections of the United States. One of the largest companies in the United States found that cement could be manufactured from a combination of blast-furnace slag and limestone, and this is now made by the company in large quantities, the product being a true Portland cement.

What Is Concrete?

Portland cement is the strongest and most lasting of all modern mortars or binding materials. When mixed with sand and stone the resulting mixture is called concrete. Being a plastic material when first mixed, it cannot be used as we use brick or stone, but must be poured into molds or forms, which hold it in place until it hardens into rock. It may be cast in any form or shape, and thus it is useful for a vast number of purposes. It will harden under water, and time and exposure to the elements merely increase its strength. The most common form in which it is used, one familiar to everybody, is in the construction of sidewalks. It is used in all great engineering projects, such as the building of dams, bridges, retaining walls, sewers, subways and tunnels. Being fireproof, large quantities of it are used in buildings and likewise on our farms, where it is extremely valuable as an enduring and sanitary material.

What Is Cement Used For?

It has been said that concrete is a plastic material, meaning that it is soft and pliable in the sense that clay or putty are plastic. For this reason it is cast in forms or molds. Sometimes it is used in the form of plain concrete, and on other occasions it is reinforced, meaning that iron rods, steel bars or woven wire mesh are imbedded in the concrete. When we speak of a “reinforced” concrete building, imagine a huge wire bird cage encrusted within and without with concrete. Place a block, beam or column of concrete upon the ground and it will bear a tremendous load, meaning that it has great strength in compression. On the other hand, if we were to place a long beam upon supports at either end, leaving the greater length of it suspended and without support, it would carry but a small load compared with concrete in compression. Therefore, in making concrete beams or girders in a building, strong steel bars are embedded in the concrete to take up what are termed the tensile strains.

This is a picture of a cement mill. Millions of dollars are invested in these great mills, which are now located in practically all sections of the country. Material is brought from the quarry to the mills, where it passes through various stages, such as grinding, burning and bagging. Expert chemists are employed to see that the cement is made exactly right. It is a very scientific matter to make a thoroughly good cement. There must be no guess work. Some mills are very large, the plant comprising a number of buildings, and some companies operate several mills in different localities. A single company supplied all of the cement used in the Panama Canal, which great project required more than six million barrels.]

This is an illustration of a method of excavating and loading marl and clay to be manufactured into Portland cement. The large bucket suspended over the cars does not gouge into the hillside as shown in the preceding picture, but descends like a huge steel hand, the metal parts opening and closing like fingers. The long derrick elevates the bucket and swings it over the train of cars.]

This is a view of the electric motors operating the grinding machines which reduce the raw material to a very fine powder. There are various types of mills or grinders, to which the material comes after going through the rock crusher. They grind it in preparation for the kilns.]

This is an ingenious machine which bags and weighs the cement. The bags are suspended as shown, and when filled and weighed by the machine are placed in barrels and shipped to their destination. Every device of this kind that will save time and labor cheapens the cost of manufacture.]

This picture shows how concrete houses or walls are built through the use of what are known as forms. In building a wall we have an inside and outside form, as shown in the picture, between which the concrete is placed. After it hardens the forms are removed. In some operations, such as the construction of a large factory building or great bridge, there is such a vast array of timber construction as to make the scene quite impressive, especially when bridge arches of great span and height are under construction.]

This is a curious example of concrete construction. It is a coal pocket, from which locomotives are supplied with fuel. Railroad companies have adopted it because of its great strength and durability.]

This is an interesting example of concrete construction. It is a large water tower which will never warp, rust or decay. In this field concrete has been of great service, whether reservoirs are constructed in the form of towers or tanks. As already stated, water does not affect the life or strength of concrete, except to improve it.]