December 25, 1885.] 



SCIENCE. 



561 



occurs in each twenty-four hours, was attacked. 

 Staff- gauges were first used, but were shortly supple- 

 mented by an ingenious self-registering gauge, in- 

 vented by Mr. Joseph Saxton, of the weights and 

 measures office, by which a continuous automatic 

 record of the rise and fall, with effects of winds and 

 storms, was kept up. These were gradually multi- 

 plied by similar instruments at carefully selected 

 points along the coast, until, in 1854, sufficient data 

 had been collected and reduced to form a theory on 

 which was based tables of predicted tides for every 

 day in the year, and for all principal ports upon the 

 Atlantic and Gulf coasts. This contribution of the 

 coast survey to the practical necessities of navigators 

 has been continued and gradually improved up to the 

 present day, and large editions of these little books 

 are yearly printed and eagerly sought for. Similar 

 tables for the western coast, founded on similar ob- 

 served data, were first published in 1870, and are also 

 continued. 



A very considerable contribution to science oc- 

 curred in 1883, when the tide-gauges of the coast 

 survey at San Francisco, Alaska, and Honolulu, all 

 indicated upon their automatic record the effect of 

 the great earthquake at Krakatoa, in the Straits of 

 Sunda, full one-quarter of the circumference of the 

 globe from the nearest tide-gauge. These earthquake- 

 waves, greatest at Honolulu, continued to impress 

 themselves upon the records for between four and 

 five days. Photographic copies were sent to the 

 Eoyal society at London by their request. 



Another contribution to science in this department 

 has been the invention and daily use, in the coast- 

 survey office, of a tide-predicting machine, which, 

 being set to represent certain elements obtained by 

 not less than a yearly observation at any place, will, 

 by simply turning a crank, predict the times and 

 heights of future tides at that place for the ensuing 

 year. This invention is by Prof. William Ferrel, 

 formerly of the coast survey, and now of the signal 

 service. 



Physical hydrography. 



Tidal currents, and the laws governing them, have 

 been studied, and the best methods of so controlling 

 them as to aid navigation by deepening channels 

 have been applied in all parts of the Atlantic and 

 Gulf coasts ; the basis of action being the coast-sur- 

 vey maps, and the organization of each commission 

 appointed to advise the best action being precisely 

 that of the coast survey. Such commissions have 

 acted, with the most useful effect, in Portland, Bos- 

 ton, Providence, New York, Philadelphia, Wilming- 

 ton, N.C., Charleston, Savannah, and other places. 

 In all cases the commission has consisted of one 

 engineer officer of the army, one naval officer, and 

 one coast-survey officer. Usually the naval officer has 

 been one who had several years of experience in 

 hydrography upon the coast survey. 



Prof. Henry Mitchell, an assistant in the coast 

 survey, has made physical hydrography his special 

 study, and has become one of the recognized authori- 

 ties upon the subject in this country. He is, and has 

 been since its formation, a prominent member of the 

 Mississippi River commission. Of the one hundred 

 and seventeen publications by the coast survey on 

 the subject of physical hydrography between 1845 

 and 1883, twenty-seven are by Professor Mitchell, 

 and all have a direct bearing upon the best methods 

 of improving the commerce and navigation of the 



principal ports and navigable thoroughfares of the 

 Atlantic and Gulf coasts. 



Magnetic observafAons. 



In the early surveys of this country, the compass, 

 with its magnetic needle, has been the principal in- 

 strument used. It still continues to be largely used, 

 especially in new settlements, and portions of the 

 country where land is of small value. In more 

 populous portions, where land has become valuable, 

 it is being steadily discarded for instruments of 

 greater precision. As a consequence of its great 

 use, observations to determine the general and local 

 magnetic variation had been made in many places 

 from the earliest period of the country's settlement. 

 As our knowledge of the subject increased, and the 

 laws governing the all-pervading magnetic principle 

 came to be better understood, observations not only 

 for magnetic variation from the true north were in- 

 creased, but apparatus was invented and largely 

 used for observing the two components of the mag- 

 netic force, and obtaining the total intensity wdth 

 which it acts upon a freely suspended magnet in any 

 locality. 



Observations of this character were commenced in 

 the coast survey in 1833, and have been kept up ever 

 since, being vigorously pursued since 1844. Small 

 amounts were also paid to outside observers, and in 

 some cases instruments have been loaned on condi- 

 tion of furnishing copies of their observations. Since 

 Professor Bache's death, this important department 

 of coast-survey scientific work has been in the hands 

 of Assistant C. A. Schott, who has, with indefatiga- 

 ble labor, made it specially his own. He has col- 

 lected and digested all detached observations from 

 every quarter of North America. The tables and 

 maps prepared under his direction, and published by 

 the coast survey, have been and are more largely 

 called for than any other pubKcations ; and the ex- 

 pressions of thanks for and appreciation of the 

 valuable practical aid they have given, have been 

 received from engineers and surveyors throughout 

 the entire country. Seventy-two publications have 

 been made by the coast survey on terrestrial magne- 

 tism, of which fifteen are by Professor Bache, and 

 forty by Assistant Schott. 



Astronomy as applied to geodetic surveys. 



When Professor Bache became superintendent of 

 the coast survey, in 1844, it possessed no instrument 

 for precise determination of latitude superior to a 

 sextant. Lieut. Thomas J. Lee and the writer spent 

 a large portion of the season of 1844 in vain endeav- 

 ors to obtain reliable results from the larger instru- 

 ments in its possession, which still remain in the 

 archives to mark the progress made in this branch of 

 ' practical astronomy.' Only one small portable transit 

 instrument for observing time belonged to the survey. 

 As rapidly as possible instruments of a higher order 

 were introduced, and better methods of observation 

 and reduction began. The zenith telescope was 

 introduced. This instrument, invented for a differ- 

 ent purpose, had been ingeniously appHed by Capt. 

 Andrew Talcott, Corps of engineers, U.S.A., to a 

 method of determining latitude, of so dehcate, pre- 

 cise, and simple a character, as to leave nothing to 

 be desired in these respects. Just at that time the 

 British association for the advancement of science 

 had published their catalogue of places of over seven 

 thousand stars, chiefly in the northern hemisphere, 



