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TIMBEB 402 TIME sulphate of zinc is used the process is termed burnettising; and the third method — the only one extensively prac- ticed in Great Britain — is creosoting. The latter consists in steeping the wood in creosote oil, from 8 to 12 pounds being required for every cubic foot of timber. Since 1882 a new process introduced by H. Aitken, of Falkirk, has been under trial — namely, the soaking of timber, ac- cording to its bulk, from 2 to 12 hours in melted napthaline. This is a volatile substance, which must so far be against its efficiency, but the results of the ex- periments are said to give good promise of success. TIMBUKTU, a city of the Sudan, Central Africa, in lat. 17° 37' N. and Ion. 3° 5' W.; 6 miles N. of the Niger at the extreme N. point of its course. The town is triangular in shape, and at present is less than three miles in cir- cumference, though formerly it was much larger. The wall or rampart which sur- rounded it was destroyed by invaders in 1826, and has not been rebuilt. The streets are for the most part straight and unpaved, with a gutter in the center. Most of the houses are of clay, and some are two stories high, a very unusual thing in Negroland. On the outskirts there are a good many conical huts of matting. Of the mosques, two are es- pecially noteworthy from their great size and imposing appearance, viz., that of Sankore in the N., and the great mosque in the W. angle of the town. The latter is 286 feet long and 212 feet wide. Tim- buktu has also two markets. The cli- mate is unhealthy, and the surrounding country being desert, or nearly so, all supplies of food are brought by the Ni- ger from Sandsanding to Kabara, the por.t of Timbuktu. The manufactures are confined to a little iron work, and to leather bags, pouches, cushions, etc., made by the Tuarick women. The place owes its importance entirely to its com- mercial situation, which makes it the entrepot for the trade between the N. and S. of the Sahara. In addition to the Niger there are two main channels by which commerce flows to Timbuktu, viz., the caravan routes from Morocco on the N., and Ghadames on the N. E, The principal articles of trade are gold in rings, salt, English calico, red cloth, cutlery, looking-glasses, rice, ne- gro corn, kola nuts (a substitute for coffee), ginger, tobacco, dates, and tea. Timbuktu was founded toward the end of the 11th century, and became known to Europeans in 1373. Pop. (1917), about 16,000. TIME. Time and space arc the two great elements with which the astronomer in the observatory has to deal; conse- quently a great part of astronomical work, and a great part of the equipment of every observatory, is devoted to the determination of time in various ways and for various purposes. Measurement of Time. — This is accom- plished by the joint work of the clock and watchmakers, and of the astronomer who makes observations of the transits of the heavenly bodies across the meri- dian to determine the necessary daily cor- rections to these instruments. For no piece of chronometric apparatus, even the best constructed astronomical clock, can begin to approach in regularity of run- ning the motions of the heavenly bodies, especially the rotation time of the earth on its axis, on which most time determi- nations depend. The principal pieces of apparatus used for keeping time are various forms of clocks and watches. Be- fore the invention of these instruments the measurement of time was very rough, the most accurate being the method of the sundial; but as this was only good in the day time and when the sun was shining, various rougher devices were employed, such as running sand in the hour glass, the water clocks, or clepsy- drae, or even a burning candle. The senseless division of the day into two periods (of 12 hours each), which was probably originally brought about by the use of the sun's shadow in the day time and something or nothing else in the night, is one of the relies of barbarism which seems to be the hardest to get rid of. Even the division into 24 hours (in- stead of decimals of the whole day, as it ought to be) is bad enough, but, on account of the radical change necessary in the construction of all clocks and watches in order to bring this about, it will probably be a long time in coming. But the small changes necessary in the dials in order that they may read up to 24 hours instead of 12 makes it surpris- ing that there is so much opposition to the proposal of the railroad managers simply to print their time tables with the day divided in that way. Different Kinds of Time. — Two differ- ent kinds of time, wath different actual lengths of the unit, are in common use — mean solar and sidereal. The mean solar day marks the average interval of the return of the sun to the same meridian. The time marked by the return of the actual sun is not uniform, and is called apparent time. The difference between mean and apparent time is called the equation of time. Mean solar time is that in common use, but the mean solar