MICROSCOPY. 119 
of civilization at which the builders of the pfuhlbauten had arrived, 
Long after came the ages of bronze and iron, and finally the 
Roman period, with its fixed dates and absolute chronology. 
rapid review of the history of humanity in Europe shows us an un- 
interrupted series of events, looking back from the Roman period, 
through the various lacustrine epochs as far as the most ancient 
remains of polished stone. But there occurs a gap. We are not 
in presence of fixed dates, and the continuity of the events alone 
gives us a perfect key to their relative antiquity. Professor Forel 
asks—has this lacuna lasted a hundred years, a hundred thousand, 
or millions of years? And, while he does not attempt to precisely 
estimate its duration, he proves convincingly that the gap is consid- 
erable, but that it is not enormously large. The age of trees which 
must have grown in the rich vegetable beds of Morges, after mould 
had been slowly formed from the débris of the pebble beds of the 
glacial period, indicates a vast lapse of time. Professor Forel 
enters at great length into certain results at which he has arrived 
after sounding the Rhône at various levels, and precisely estima- 
ting the amounts of mud which the river annually transports. He 
considers that a space of 300,000 years is necessary in order fo fill 
the lake of Geneva, and that in time the lake will be entirely filled 
up. His conclusions, in fact, are that the space of time which 
separates the archeological ages of the reindeer and of the red 
deer (paleolithic and neolithic epochs) is considerable, and ought 
to be counted by thousands of years; it is not infinitely great, and 
ought not to be counted by millions of years. . 
MICROSCOPY. . 
t Power” or Lenses.—For some three or four years some 
American microscopists have been calling attention to the “ decep- 
tion,” commonly practised by most working opticians in calling the 
“power of their instrument less than it really is— i. e., calling an 
objective a quarter-inch when its focus is really but one-fifth or 
one-sixth of an inch + or an eighth when actually a “ one-ninth or 
one-tenth,— and some now approach to one-twelfth.” 
In the “ Monthly Microscopical Journal” for December, 1871, 
Mr. F. H. Wenham writes a paper in reply to one of Mr. E. Bick- 
nell’s on this subject in which he takes Mr. Bicknell to task for 
exposing the deception,—and admits the truth of the charge. 
a ie 
