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MINERALOGY

What is the structure of a hailstone? 824.

What is the probable explanation of hailstorms? 824.

What is snow? 1773.

How is snow formed? 1773.

What causes the whiteness of snow? 1773.

What is meant by the "snow line"? 1773.

Why does snow never collect to an indefinitely great depth? 1774.

LUMINOUS  PHENOMENA. Where does the aurora borealis occur? 140. How does it appear in intermediate latitudes? 140. How does it appear in higher latitudes? 140. What makes it seem probable that auroras are produced by electrical

discharges? 140.

What sort of a spectrum does the aurora present? 140. Where are auroral displays most frequent? 140. What is lightning? 1069. Who established  the  connection  between  electricity  and  lightning?

1069.

Is the source of electrical charges known? 1069. What is the rainbow? 1582. Of what does the rainbow consist? 1582. What are the two bows called? 1583. Who first gave the explanation of the rainbow? 1583. Who completed this explanation? 1583. What is a mirage? 1239. What is the cause of a mirage? 1239. In what different ways does the object appear? 1239. What is the explanation of this? 1239. What ship was discovered by means of a mirage? 1239. What is twilight? 1960.

If there were no atmosphere, what would become of the twilight? 1960. In the polar regions how long does the twilight last? 1960. What theories are there as to the matter in the atmosphere that thus

reflects the sunlight? 1960.

MINERALOGY

What does the science of mineralogy embrace? 1230.

What parts of the subject are dealt with in physical mineralogy? 1230.

What does chemical mineralogy consider? 1230.

What is shown in descriptive mineralogy? 1230.

When was it that minerals began to be properly studied and classified? 1231.

How were minerals grouped in the system presented by Mohr? 1231. *What methods are now used? 1231.

How do minerals vary in hardness? 1231.

What mineral exhibits different shades of five different colors? 1231.

What are the six systems according to which all crystals, natural and artificial, are classified? 1231.

What is meant by "twinning"? 1231.

What are the four principal ways in which minerals have been formed? 1231.

What is pseudomorphism? 1231.

By what process has petrified wood been formed? 1231.

Where is the topaz found? 1923.

Where is the tourmaline found? 1928.

How did the amethyst get its name? 63.

How are pearls obtained? 1435.

Where are the finest specimens of onyx found? 1168.

Where is the most celebrated opal now found? 1385.

Where  is the turquoise mostly found? 1958.

In whose possession are the finest specimens of turquoise supposed to be? 1958.

2387