Page:The Construction of the Wonderful Canon of Logarithms.djvu/100

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an arc, to find the logarithm of its versed sine.

Conversely, given the logarithue of a versed sine, to find its arc.

Add the known logarithm of the required versed sine to the logarithm of 30°, viz, 693147, and half the sum will be the logarithm of half the arc sought for.

Thus let 35791 be the given logarithm of an unknown versed sine, whose arc is also unknown.

To this logarithm add 693147, and the sum will be 728938, half of which, 364469, is the logarithm of 43° 59′ 33″. The arc of the given logarithm is therefore 87° 59′ 6″, and its versed sine is 9648389.

Again, let a negative logarithm, say —54321, be the known logarithm of the required versed sine. To this logarithm