VI 



PREFACE. 



carried on in the same manner as is there described, hourly eye observations being 

 made by day and night. A description of the mode of observing for each instrument 



f %M 



Fig. 2. — the ben nevis observatory in winter. 



Fig. c 



6. THE GREAT CLIFF UN BEN NEVIS. 



I /■'< (mi Poullon's Series. 



will be found in the Introduction (p. 1 et seq.); but it may be here stated that the chief 

 difficulties that the observers have to overcome, are the deposition of ice crystals from 



