June 6, 1901] 



NATURE 



137 



declination, horizontal force and dip have been made as in 

 former years. 



Tlie regular determinations of magnetic declination, horizontal 

 force and dip have been made with the new declinonjeter, the 

 Gibson deflexion instrument, and the Airy dip circle mounted 

 in the new Magnetic Pavilion. 



The principal results for the magnetic elements for igoo are 

 as follow : — 



Mean declination ... ... ... 1 6° 29' -o West. 



., , • . , r f 4'ooi4 (in British units). 



Mean horizontal force 1 7 o ,„ ,• at . • ■- I 



( I 0450 (in Metric units). 



Mean dip (with 3-inch needles) ... 67° 8' 27'. 



These results depend on observations made in the new 

 Magnetic Pavilion, and are free from any disturbing effect of 

 iron. 



The magnetic disturbances in 1900 have been few in number. 

 There were no days of great magnetic disturbance and eight of 

 lesser disturbance. 



The question of the possible effect of disturbances from 

 electric railways on the magnetic work carried on at the Royal 

 Observatory has required very careful consideration in regard 

 to the conditions under which electric traction may be used 

 without injuriously affecting the magnetic registers. 



It may be remarked that the French magnetic observatory 

 at St. Maur is in much the same position as Greenwich in 

 respect to electric tramways, and recently M. Moureaux, in 

 charge of that observatory, has found that copper "dampers" 

 (such as have been in use at Greenwich for sixty years, but had 

 not previously been applied to the magnets at St. Maur) reduce 

 the vibratory disturbances from electric tramways to about one- 

 tenth of their amount. This has recently been verified at 

 Greenwich by the converse process of removing the copper 

 "dampers" which are in regular use with the declination and 

 horizontal force magnets, when it was found that the disturb- 

 ances from existing electric railways were increased to about 

 ten times their amount. It is proposed to apply a " damper " 

 to the vertical force magnet, the need for which has not hitherto 

 been felt, and it is possible that the "dampers" for the other 

 two magnets may be improved by the use of copper of much 

 higher conductivity than was obtainable when they were made 

 sixty years ago. 



It is hoped, however, that, in the event of future proposed 

 electric tramways, regulations will be laid down by the Board of 

 Trade to secure adequate protection for the magnetic work at 

 Greenwich, which has now been carried on continuously on the 

 same general system for a period of sixty years, and which could 

 not be transferred to another site. 



Meteorological Observations. 



The meteorological instruments are all in good order. The 

 registration of atmospheric pressure, temperature of the air, 

 and of evaporation, pressure and velocity of the wind, rainfall, 

 sunshine and atmospheric electricity has been continuously 

 maintained. 



The mean temperature for the year 1900 was 50° '5, being 

 i°o above the average for the fifty years 1841-90. During the 

 twelve months ending 1901 April 30, the highest temperature 

 in the shade (recorded on the open stand in the Magnetic 

 Pavilion enclosure) was 94'"© on July 16. The highest temper- 

 ature recorded in the Stevenson screen in the enclosure was 

 gi'^S, and in that in the Observatory Grounds 93° '4 on the same 

 day. This is the highest shade temperature recorded in July 

 since 1881. It has been twice exceeded in July in the sixty 

 years 1841-1900, viz., on 1881 July 15, when the temperature 

 reached 97°-!, and on 186S July 22, when it was 96°-6. A 

 reading of 94° o was also recorded on 1876 July 17. The 

 monthly mean temperature for July was 66° '6; it has been 

 exceeded only four times in the preceding sixty years, viz., in 

 1852, 67°-o; 1859, 6S°-9; 1868, 68°-i ; and 1876, 66 7. The 

 month of December was also exceptionally warm, the mean 

 temperature for the month being 45°'7, which is 6''o in excess 

 of the fifty years' average. This value has been exceeded three 

 times in the preceding sixty years, viz., in 1S52, 47°'6 ; in 186S, 

 46' •! ; and in 1898, 45 8. The lowest temperature of the air 

 recorded in the year was 20° 4, on February 14. There were 

 forty-seven days during the winter on which the temperature 

 fell below 32°, a number slightly below the average. 



The mean daily horizontal movement of the air in the twelve 

 months ending 1901 April 30 was 29S miles, which is 17 miles 



NO. 1649, VOL. 64] 



above the average for the preceding thirty-three years. The 

 greatest recorded daily movement was 973 miles on January 27, 

 and the least 72 miles on December 23. The greatest recorded 

 pre.ssure of the wind was 34'4 lbs. on the square foot, and the 

 greatest hourly velocity 54 miles, both on January 27. 



The number of hours of bright sunshine recorded during the 

 twelve months ending 1901 April 30, by the Campbell-Stokes 

 instrument, was 15 13 out of the 4457 hours during which the 

 sun was above the horizon. 



The rainfall for the year ending 1901 April 30 was 20'22 

 inches, being 4^32 inches less than the average of fifty years. 

 The number of rainy days was 151. The rainfall has been less 

 than the average in each year since 1894. 



The remaining portion of the report deals with the work done 

 in the remaining departments — namely, chronometer, time- 

 signal, &c. It may be here remarked that arrangements have 

 been made for a re-determination of the Greenwich- Paris longi- 

 tude in conjunction with observers from the Paris Observatory, 

 two of the four portable transit instruments used in former 

 longitude work being available for the French observers, and 

 the other two for the English. 



It has been arranged with M. Loewy that the first part of the 

 longitude observations shall be m.ade in October next, and the 

 second part in the spring of 1902. 



The eclipse of May 28, igoo. was observed by the Astro- 

 nomer Royal with Mr. Dyson and Mr. Davidson in Portugal, 

 while this year Mr. Dyson, with the assistance of Mr. Atkinson, 

 went to Sumatra, and Mr. Maunder to Mauritius, for the recent 

 eclipse of May iS. 



In his general remarks the Astronomer Royal points out the 

 great pressure of work that has fallen on all members of the staff 

 during the past year. Two eclipse expeditions have been pre- 

 pared and sent out, the revision of Groombridge's Catalogue for 

 1810, in connection with the Greenwich Second Ten-^'ear 

 Catalogue (1890), the transfer of books and records to the New 

 Observatory, and the rearrangement of the library and record 

 rooms, all have added considerably to the ordinary work of the 

 Observatory. Finally, he points out that within the last five 

 months one-third of the whole staff of computers have left the 

 Observatory for other posts and have had to be replaced by 

 boys new to their work. Such an extensive change in the 

 temporary staff has, to a certain extent, disorganised the work 

 and has thrown a great strain on the assistants, who are charged 

 with carrying it on under such difficult conditions. Considering 

 the training and experience required in the varied work which, 

 at Greenwich, has to be done by computers, a greater degree of 

 permanence in the staff appears to be necessary for the continued 

 efficiency of the Observatory. 



THE MECHANICAL FORCES OF NATURE 

 AND THEIR EXPLOITATION. 

 ""PHE question of the probable end of the world's coal supply, 

 in the not far distant future, is one which has in recent 

 years been the cause of much discussion. In connection with 

 this subject a pamphlet published by the Urania Gesellschaft of 

 Berlin, on " Die mechanischen Naturkrafte und deren Verwer- 

 tung," by F. Reuleaux, is of interest. In a clear and popular 

 manner the author traces and explains the gradual utilisation 

 by mankind of the various natural forces, from the ancient 

 Assyrian water wheel to the installations of Niagara, and the 

 Parsons steam turbine. It has been calculated that the supply 

 of coal in England can only last at the most 200 years more ; and 

 though the coal-fields of the other European countries have not 

 been used to the extent that the English ones have, still their 

 eventual exhaustion can alre.idy be anticipated. The total con- 

 sumption is now about 600 million tons per year, or, measured 

 as a volume, about 500 million cubic yards. Assuming a yearly 

 increase of 5 per cent, (it is at the present moment greater than 

 this) this would mean that during the present century 6.V billion 

 cubic yards of coal will be taken from the earth's coal mines. 

 A cube of this volume would have a side over ten miles long. 



It may be urged that this is not a matter of immediate import- 

 ance ; still, in considering the future industrial state of the 

 world one must admit that great changes must take place, and 

 that countries which have been indebted for their growth to 

 their natural resources of povver in the form of coal must give 

 way to those countries where power is supplied in another form. 

 On examining the natural sources of power, one sees that really 



