58 REPORT — 1886. 



given in the ' Natural Philosophy ' merely remain, then, as generally con- 

 firmatory of Thomson's conclusion as to the great effective rigidity of the 

 earth's mass. 



There ai'e but few ports for which a sufiBcient mass of accurate tidal 

 observations are accumulated to make the detection of the 19 -yearly tide 

 a possibility. 



Major Baird has, however, kindly supplied me with the values of the 

 mean sea-level at Karachi for fifteen years. They are plotted ont in the 

 annexed figure. The horizontal line reoresents the mean sea-level for the 

 jjeriod from 1869-1883, and the sinuous curve gives the variations of 

 mean sea-level during that period. The dotted sinuous curve gives the 

 annual variations for a portion of the same period for Bombay. The full- 

 line sweeping curve has ordinates proportional to — cos 83, and shows the 

 kind of curve which we ought to find if the alternations of sea-level were 

 due to the 19-yearly tide. 



It is obvious at a glance that the oscillations of sea-level are not due 

 to astronomical causes. 



At Karachi (lat. 24° 47') the 19-yearly tide is 



-0"-0138cosS. 



The figure shows that the actual change of sea-level between 1870 and 

 1873 was nearly 025 feet, and this is just about nine times the range of 

 the 19-yearly tide, viz., 0-028 feet. 



It is thus obvious that this tide must be entirely masked by changes 

 of sea-level arising from meteorological causes. 



It seems unlikely that what is true of Kai-achi and Bombay is untrue 

 at other ports, and therefore we must regard it as extremely improbable 

 that the 19-yearly tide will ever be detected. 



G. H. D. 



Report of the Committee, consisting of Professor Crum Brown 

 (Secretai-y), Mr. Milne Home, Mr. John Mdrrat, and Mr. 

 BucHAN, afpointecl for the pui^ose of co-operating with the 

 Scottish Meteorological Society in making Meteorological Obser- 

 vations on Ben Nevis. 



Ddeing the past year the work of the Ben Nevis Observatory has been 

 carried on by Mr. Omond and his assistants in a way that leaves nothing 

 to be desired. The twenty-four daily eye-observations have been made 

 uninterruptedly ; and it deserves to be recorded that, as regards the out- 

 side observations, no hour has been omitted even on those occasions when 

 the wind blew furiously at rates considerably above 100 miles an hour. 



The eye-observations, taken five times daily at the sea-level station at 

 Fort William, have also been made with the greatest regularity by Mr. 

 Livingston ; and with these are conjoined the continuous records of the 

 barograph and thermograph, the results of which are so valuable in 

 checking and discussing the observations. 



For the twelve months ending May 1886 the mean temperatures and 

 pressures at the Ben Nevis Observatory and Fort William were these : — 



