lamely? Their failings, with their reproaches, now sleep with them in the grave. Man wars not with the dead. It is a trait of human nature, for which I love it. LOVE THY MOTHER. mirror back, return. stroke, the stroke of death. 1. Love thy mother, little one! 2. Gaze upon her loving eyes, And mirror back her love for thee,- 3. Press her lips the while they glow 4. Pray for her at eve and morn, That Heaven may long the stroke defer,- THE THERMOMETER. ther-mom-e-ter, an instrument for measuring the degree of heat. de-gree, measure or extent. ac-cu-ra-cy, with exactness." 1. The degree of heat in any substance is called its temperature, which varies from time to time, according to circumstances. Boiling water, for example, contains so much heat that it scalds the skin; but when removed from the fire, the water gradually becomes less and less warm, until at last it contains so little heat that it cools the hand instead of scalding it. 2. The thermometer is used to show whether one thing is warmer or colder than another, and how much warmer or colder. The name simply means heat-measurer. You can all tell whether anything is warm or cold; at least, you think you can. But strange as it may seem, we cannot always trust the accuracy of our sensations. 3. Here is a way of ascertaining :-Fill three glasses with water-the first with cold. water; the third with very hot water; and the second, or middle one, with water only lukewarm. Put one finger into the hot and another into cold water, and keep them there for a little time. Then plunge both into the lukewarm water. The finger from the cold bath will find the change pleasantly warm, whereas the finger from the hot glass will find it as pleasantly cool. FAHRERHEIT. -50 40 4. A person comes into a warm room from the open air on a cold day, and exclaims, "How warm it is here!" Another person enters the same room from one still warmer, and cries, "How cold it is here!" The first person gains heat, and therefore calls the room warm; the second loses heat, and calls it cold; while, in reality, the air of the room, all the while, is at the same degree of temperature. -30 1-20 1-10 LINC -10 5. A nurse prepares water for a child's bath, and measures the heat by the feeling of her hand; but she learns from the quick and sudden cry of the child, when placed in the bath, that what seemed warm to her is cold to the child. 6. These examples show that our sensations are not always a true test of temperature; and thus, if we wish to measure heat and cold accurately, we must have some instrument made for the purpose. Such an instrument is the thermometer. 7. It was long ago noticed that bodies expand, or swell out, when they are heated; and that they contract, or shrink into less bulk, when they are cooled. This led to the construction of the thermometer; for to measure the expansion or contraction of a substance is the same as to measure the quantity of heat that has produced this effect. 8. The thermometer is a fine glass tube with a bulb blown at one end of it. It is nearly filled with a liquid. The liquid most generally used is that lively, silvery-looking metal, quicksilver; or, as it is often called, mercury. This liquid metal is found to be very sensitive to changes of temperature. It is therefore a suitable means for measuring heat and cold. 9. The thermometer tube is sealed up, not with sealing-wax, but by melting the glass at the end. After the thermometer is made, it requires to be marked, in order to note the rising or falling of the mercury, and thus to show how much one body is warmer or colder than another. This marking is called its scale. 10. The little spaces you see on the thermometer are called degrees, and marked with a little circle thus (). Hence 32° is read thirtytwo degrees. The scale of a thermometer can either be marked on the glass itself, which is the neatest and most exact plan; or it can be marked on a piece of wood, metal or some other substance fixed to the side of the tube. 11. The first thing to be done for the scalemarking is to fix, if we can, upon two points that never alter. Now it has been found out that ice melts always at the same degree. That is fixed point number one. Secondly, that water boils at a certain uniform heat. That is fixed point number two. 12. Accordingly, our thermometer is first plunged into water in which ice is melting, and the tube is marked where the top of the mercury then stands. After this, the instrument is put into a steam bath, and again marked according to the position of the mercury. 13. The space between these two fixed points is divided in different ways. In France they have divided it into 100 equal parts, which is a very handy mode of division. In Germany they use a scale divided into 80 equal parts. 14. In England, the plan is again different. About 150 years ago a German, named Fahrenheit, divided the space between the two fixed points into 180 equal parts. Accordingly, the English thermometer has as many degrees as the French and German scales put together. 15. One end of the proper scale of all three is the melting point of ice, the other the boiling point of water. You would naturally suppose that at the ice-melting point you would see zero (0) marked, to begin the scale. And so you do in the French and German thermometers. But on the English scale you see the number 32° marked. And this is the reason. |