1871.] 



President's Address. 



53 



The existence of a Lunar Atmospheric Tide, as indicated by differences 

 of barometric pressure corresponding systematically to differences of 

 the moon's position relatively to the meridian, has received a further con- 

 firmation by the discussion by Mr. Bergsma, of the Royal Netherlands 

 Observatory at Batavia, of a series of hourly observations of the ba- 

 rometric pressure at that Observatory, extending (Sundays excepted) from 

 January 1866 to January 1869, made specially with a view to this in- 

 vestigation. The discussion is on the same plan (slightly modified and 

 thereby improved) as that by myself of the observations at St. Helena, 

 from October 1843 to September 1845 inclusive, in the Phil. Trans, for 

 1847 ; and that by Captain Elliot of the observations at Singapore, from 

 1841 to 1845, in the Phil. Trans, for 1852. The results, as regards the 

 existence of the periodic tide, are substantially the same in the three cases, 

 but may probably be more approximatively exact in value in the more recent 

 investigation. Prom the observations of the three years at Batavia, Mr. 

 Bergsma finds that the Lunar Tide has at that station two maxima and 

 two minima. The two highest barometric pressures are those for the 

 lunar hours 1 and 13, being the hours following the two passages of the 

 moon through the meridian. The two lowest pressures are those for the 

 lunar hours 7 and 19, being those following the two passages of the 

 moon through the horizon. The means found for each of the years 1866, 

 1867, and 1868 show nearly the same features as the means for the 

 three years. The difference between the mean of the two maxima and 

 the mean of the two minima is 0*107 millim. at Batavia : this dif- 

 ference was found for St. Helena 0-094 millim., and for Singapore 0*145 

 millim. 



The Pellows will remember that in my two last Addresses (for 1869 and 

 1870) I referred to the valuable memoirs of Professor Heer, of Zurich, on 

 the fossil plants brought of late, at various times, from the Arctic regions. 

 Professor Nordenskiold revisited the shores of West Greenland in 1870; 

 and on learning that he had given the principal geological facts and fossils 

 collected in that expedition to Professor Heer, I lost no time in communi- 

 cating with the latter gentleman, and received from him (through Mr. 

 Robert Scott, P.R.S., Director of the Meteorological Office) a reply, which 

 appeared to me so interesting that I placed it in the hands of Sir Charles 

 Lyell, asking him, if he would be so kind, to furnish me with a notice suf- 

 ficiently brief to be included in this Address. He has done so, and I sub- 

 join it in his own words : — " The first voyage of Parry in 1819-20 made 

 " the naturalist acquainted with the marvellous fact that plants similar to 

 " those of our ancient coal once flourished in Melville Island, lat. 75° N. ; 

 " and now we learn more exactly, from the fruits of Nordcnskibld's late 

 " Expedition, that the arctic plants of that early Palaeozoic period are not 

 " only traceable over a wide area, but that not a few of them arc identical 

 " with European species ; and it is remarkable that the specimens which 

 " have been brought from these high latitudes are equal in size and show 



