We would advise each person desiring to sell, to
send a sample first, with a statement of the quantity offered.
* * * * *
Dr. Zintgraff of Bonn has taken a phonograph with him to Africa. He
intends to bring home phonograms of the savage dialects which he will
hire the natives to speak into the machine.
* * * * *
[NATURE.]
DETERMINING THE MEAN DENSITY OF THE EARTH.
In _Nature_ for March 5 (p. 408) Prof. Mayer suggests an improvement in
our method of determining the mean density of the earth, from which it
appears that our plan has not been properly understood. This
misunderstanding, no doubt, has arisen from the incomplete description of
our method given in the _Nature_ (Jan. 15. p. 260) report of the
_Proceedings_ of the Berlin Physical Society, which report was probably
the only source of information accessible to Prof. Mayer. We are led
therefore to give a short description of our method.
Let H I K L represent a section of a cubical block of lead, about two
meters in the edge, and weighing 100,000 kilos. The balance, A B C, is
placed in the middle of the upper horizontal surface.
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