We are able to hear easily through the walls of many rooms because the material used in those walls are good conductors of sound. We know that some things are better conductors of heat than others, and just in that same way, some things conduct sound better than others. Wood has been shown to be an even better conductor of sound than air. Most of us have stood at the foot of an overhead trolley pole to see if we could hear a car coming, and we know that the reason we did this was because we could hear the wire humming, when we put our ears against the pole, even though we could not hear any sound in the air. When we are in a room that has wooden walls we can hear sounds in the next room very plainly, not because the wall is thin, but because the wood in the wall is a good conductor of sound. Other walls made of different kinds of material, are not as good conductors of sound. While you may hear through them, you cannot hear as plainly as you can through a wooden wall. What is a Diesel Engine Like? The Diesel engine has caused a great deal of comment of late years because of the spectacular uses to which it has been successfully applied. A specially constructed Diesel engine was probably the chief aid in the accomplishment of the first submarine trans-Atlantic voyage by the German submarine “Deutschland.” It is an oil engine which was invented by Rudolph Diesel in 1893. The engine operates at compression pressures very much higher than those used in any other internal combustion engines, and it dispenses with the usual igniting devices by rendering the air charge incandescent by compression. [Illustration: THE DIESEL ENGINE] The efficiency of the Diesel engine is high, and it can use low grades of fuel, but it has the disadvantage of greater weight per horse-power than other engines. It has found increasing favor for use in marine propulsion, and in 1913 was adapted to high-speed railway service, and put into use in Germany. What does the Sheep-Grower Get for the Wool in a Suit of Clothes? A man’s ordinary three-piece fall suit has about nine pounds of wool in it. Such a suit might cost somewhere between twenty and forty dollars, depending on whether it was bought ready made or whether it was made to order. If the price was questioned, the retailer would probably explain that it was all wool and that the wool cost was the reason it was expensive, and still the sheep-man who raised the wool only received an average of about eighteen cents a pound, or $1.62, for all the wool used on the suit. Of course, the largest part of the cost of a suit of clothes is really accounted for by the cost of transportation, weaving, tailoring and selling, but we must all agree that the sheep-man who tends the flock all winter and cuts the wool in the spring is not to blame for high prices. The Story in a Silver Teaspoon[16]