emperor anything he might wish for, as a reward for his marvelous invention. "Your subject," said the inventor with becoming humility, "is already sufficiently rewarded by the pleasure he has afforded your majesty; but, since your majesty insists, he will be satisfied with a few grains of rice : one for the first square of the chess board, two for the second, four for the third, eight for the fourth, and so on to the sixty-fourth square." The reader may amuse himself by finding the number and the value of these "few grains of rice." *

We have now to consider a problem of frequent occurrence relating to decreasing geometrical progressions. Let us take the progression

a, ar, ar2, ar3...,

The applications of geometrical progressions to mechanical and physical problems are very numerous; but space does not allow us to give any illustrations at present. As is the case with arithmetical series, geometrical series are often employed in investigations that would otherwise require the use of the higher mathematics, and for this particular purpose, formula (8) is of great value in the determination of the limit (the true value) of the sum of an infinite number of decreasing terms.

A

MAN'S house may be likened unto a mirror-reflecting the character of the indweller. Bacon says, "Houses are built to live in and not to look on: Therefore, let use be preferred before uniformity, except where both may be had."

In this age of hurry-scurry-where every man seems to be striving, as in a race, with the devil as a close second-it is difficult to obtain a well constructed house, in the full sense of the term.

The owner who is fortunate enough to obtain a house that is well built has good reason to express his praise of the architect, contractor, and artisans. Ian Maclaren aptly specifies that, "He hath done a great thing who hath built a good house, a house where people may live with self-respect, and whose very walls will stimulate them to do their own work better, because one very hand they see the witness of an honest man's handicraft."

A

VISITOR to the World's Fair at Chicago in 1893 stood gazing at the water from one of the numerous bridges spanning the many lagoons for which the "Great White City" was famous. Suddenly, and without a warning sound, a slender object darted from beneath the bridge, causing the visitor to start with fright, and later to laugh at his fears. The slender object was an electric launch gliding through the water without sound or tremor.

It was at the Fair that the electric launch practically saw its birth, and since 1893 it

Twenty-nine electric launches were used upon the inland water courses at the World's Fair. A good illustration of one of these boats is shown in Fig. 1. These launches were capable of carrying 30 passengers, and with motors having between 6 and 8 available horsepower, made the entire trip of 4 miles, including stops, in 45 minutes. The speed controller was so arranged that four speeds were available when going ahead, and two speeds when going astern. boat was supplied with an air whistle, operated by a small hand pump, for signal pur

Each

has become a regular factor among pleasure craft. Although not suitable for voyages of any great extent, still, as a yacht tender and for short voyages, during which the launch will never be at any great distance from the source of power supply, it is an ideal craft. No licensed engineer or pilot is needed, and, in fact, a person without the least mechanical knowledge may operate one satisfactorily. The storage battery which supplies the current can be charged from any source of direct current, and by the assistance of a rotary transformer an alternate current may also be used. For isolated places, the windmill or the gasoline engine is perhaps the most available for driving a charging dynamo; or, where a small stream is at hand, water-power would be the most convenient.

poses, and the shrill scream of these whistles was the only sound to warn other craft of the approach of the electric launch.

Fig. 2 shows the arrangement of the storage cells and the electric motor in a western type of electric launch. The cells b, b are placed on either side of the boat beneath the seats. The motor M is shown at a point near the center of the boat beneath the floor. It is usually of the four-pole type, wound expressly for slow speeds so that the propeller shafts can be connected directly to the armature of the motor without the use of reducing gears, thus avoiding the annoying roar which gears nearly always produce. The thrust bearing at t, usually provided with ball bearings, prevents an endwise motion of the shaft. The propeller shaft

passes through a tube at f, while a form of packed joint at g, called a stuffingbox, prevents water from entering the boat around the shaft. By setting the shaft s at an incline, as shown, the propeller P is brought well below the surface of the water, giving it a better grip than if it were nearer the surface, and insuring the propeller against frequently rising out of the water when the boat is "pitching." The motor is controlled either by means of a hand wheel, as shown

at c, or by means of a handle c', as illustrated in the small sketch at the right of the figure. The operation of a controller can be understood by referring to the diagrams in Fig. 3. A set of 20 cells is shown in the diagram, divided into 4 groups of 5 cells in each group. Each group is marked with a separate letter. For instance, group A has all the cells in the group marked with the letter A. This group is an example of all; the cells are connected in series the positive terminal of one cell is connected to the positive terminal of the next. A conductor is attached to the end terminal of the right-hand cell, say the negative, and to the positive terminal of the lefthand cell. These conductors, marked g and h, are then connected to contact points on

full lines nections by dots and dashes and the multiple connections by short dashes For the reader who is not familiar with wiring plans it should be stated that, where one wire crosses another without being in electrical contact, the cross is indicated by a half circle.

the series-multiple con

The electric launches in use at the World's Fair have been superseded by the launch shown in Fig. 4. In this style of launch both motor and batteries are placed beneath the floor, giving the roomy cockpit shown in the figure. A unique innovation is shown in the substitution of wicker chairs and tables for the usual seats along the sides of the cockpit, as the open space is called.

little attention. The whole is enclosed in a box lined with sheet lead, thus rendering the motor proof against moisture. Both propeller and propeller shaft are made of bronze, in order to resist the corroding action

for a continuous run of from 5 to 6 hours. If the runs are intermittent, the total distance will be the same as if the boat was run continuously for 5 or 6 hours. At lower speeds, the charge will last much longer, but fast running uses up the charge much more rapidly. Recharging takes from 4 to 6 hours, according to the amount of current that has

FIG. 4.

HOME STUDY.

of salt water, which would soon destroy them if made of iron or steel.

The storage battery may be of any good type, of which there is a number on the market. They are invariably enclosed in hard-rubber cells having a tight-fitting cover, so that the battery liquid will not splash out and damage the woodwork of the launch.

In order to enable the operator to know the condition of his batteries at any time, a combined voltmeter and ammeter is of great assistance. This acts as an indicator, telling him just how much reserve power he has in his battery at any time; and it will frequently prevent his having to tie up to a dock or to

ask for a tow because of the batteries being exhausted. By its use the operator may also guard against exhausting the battery to such an extent as to injure it.

The tabulated data in next column regarding a common type of electric launch, will probably be of interest to the reader.

For short spurts, these boats are capable of speeds about greater than those given in the table. The speeds given can be kept up

been used since the previous charge. Usually, these boats can be run all day by making use of the time that they lie at the docks for recharging. The charging switchboard may be provided with an automatic switch, so that the batteries may be connected to the charging terminals when tied up for the night, and the current broken by the switch as soon as the batteries are fully charged.

A great number of these craft are now being used as yacht tenders and at numerous summer resorts. They are especially applicable for electric street railways having access to a body of water. Trolley parties

ASTOR OIL.-This is also produced in India, the lower qualities being used in soap making. It is extensively used in medicine as a purgative-the oil used for this purpose being pressed out without heat. The castor oil plant has been transplanted to various suitable climes, and is largely grown in some of our western states, the manufacture of this oil being engaged in on a large scale in Illinois. The oil is extracted by heat and pressure; after two or three repeated pressings and corresponding yields of oil (of diminishing quality) the mass is treated chemically, as in the case of palm oil, a little more being thus extracted. The first yield is used medicinally, as little heat as possible being used in its extraction; the other qualities are used for lubrication, etc. Both these kinds have to be purified before use.

Cottonseed Oil.-Here again, the United States are right ahead, there being several mills in most of the southern states devoted to the production of oil from this seed. Nearly half a million tons of cottonseed are treated annually for the sake of the oil alone. As regards the process employed: The seeds after growing, first of all have the remaining fiber removed from them, and are then pressed into cakes; they are then put into steam-jacketed vessels and stirred up in the dry heat thus obtained. This causes the oil to be freed from the cells, the hot mass then being put into bags and treated in a hydraulic press, and the oil thus extracted. The dry cake then remaining is used as food for cattle; 100 pounds of seed yield about 2 gallons of oil.

Linseed Oil.-The seed from which this oil is extracted is grown in India and Russia; this oil is much used as a dryer" in paint manufacture. It is claimed that when grown in a cold climate its drying properties are increased, but its color spoiled. The oil is extracted similarly to the other oils already described.

Hempseed Oil.-The hemp plant is chiefly valuable for the fiber obtained from it; it is from this that our well known hemp ropes are made. The oil is extracted in the same

* Begun in the September, 1898, Number.

way as the other seed oils already described, and is chiefly used for lighting and soap making.

Palm Oil.-This is obtained from the outside covering of the palm fruit and is chiefly derived from Africa. The cases, or shells, containing the nuts are thrown into heaps and exposed in the open air, being left thus for 8 or 9 days. This renders it an easy matter to separate the nuts, which are then thrown into holes several feet deep, lined with leaves of the plantain tree; the holes are then covered over and left for several weeks, until the contents are decomposed. The stuff is then taken out and well beaten, until the pulp is removed from the nuts, after which it is boiled until the oil is extracted. The longer the nuts remain buried, the thicker the oil will be, but the quality and odor will be inferior. The oil is then taken down to the coast to await an opportunity of shipment to Europe and America. It is used in candle and soap making, and also in tin-plate works; as is doubtless generally known, the "tin plates from which our domestic and other utensils are made, are only iron sheets rolled out very thin and coated with tin; these sheets are removed direct from the oil bath to the tanks of molten tin in which they are to be dipped. As this oil does not dry quickly, it is well adapted for this purpose, preserving the surface of the iron from being oxidized (rusted) before the tin has been applied. It is also very largely used in the manufacture of wagon grease, for railroad freight cars, etc.

Cocoanut Oil.-This is extracted from the fruit of the cocoanut palm, which is found in most tropical countries. There are various native processes for extracting the oil, and, as in the case of palm oil, they are rather crude and wasteful. When first extracted, in tropical climes, the oil is white and almost as thin as water, but when taken to cold countries, it solidifies to the consistency of lard, becoming at the same time opaque. It is used in the East Indies for cooking, when fresh, and for soap making, etc. when stale and rancid. It was at one time very largely