xcviii. PRESIDENT'S ADDRESS. 



Purbeck beds at Portland will give a local interest to a valuable 

 memoir on these fossil plants lately published at Washington 

 on the Mesozoic American species and others, which throws 

 much light on their methods of flowering and other points. 

 A new fern of the genus Tubicaulis of some importance has 

 been found in the coal measures, and the President of the 

 Botanical Section of the British Association calls attention 

 to the great loss to science that arises from the fact that so 

 many of the specimens of coal fossils in museums and elsewhere 

 are not labelled with particulars of locality and horizon. 

 Careful and accurate labelling in all branches of science is 

 important ; and the want of it may lead to serious losses of 

 knowledge in the future. This fact is probably far more 

 realised and acted upon now than formerly, but there is still 

 room for improvement. 



ASTRONOMY. 



The records of some of the ancient eclipses are sufficiently 

 definite and well dated to have formed the basis for calculations 

 in which it has recently been found that, by allowing an 

 acceleration of u seconds per century for the moon and 4 

 seconds for the sun, the conditions and dates of these eclipses 

 can be worked out to agree with historical accounts. These 

 accelerations might be caused by the motion of the earth 

 through a resisting medium or a lengthening of the day by 

 one two-hundredth part of a second in a century. Without 

 historical aid it would seem impossible to deal with these 

 extremely minute changes. Certain difficulties involved in the 

 well-known nebular hypothesis of Laplace have led to the 

 propounding of the planetesimal theory in its place, which 

 assumes that the nebula from which the solar system was 

 developed was not gaseous, but consisted of innumerable 

 minute planetoid bodies, revolving each in its own orbit, as 

 is probably the case in certain existing nebulae which do not 

 show a gaseous spectrum. In these the particles are much 

 closer together at certain parts, and it is by the still further 



