342 FEROUSON'S LECTURES. 



LECT. of whose gnomon must be in the very same situation 



>^v^/ that the axis of the globe was, before it was taken out 



of the horizon : that is, the gnomon must make an angle 



with the plane of the dial, equal to the latitude of the 



place for which the dial is made. 



If the pole of the globe be elevated to the co-lati- 

 tude 194 of the given place, and any meridian be brought to 

 the north point of the horizon, the rest of the meridians 

 will cut the horizon in the respective distances of all the 

 hours from XII, for a direct south dial, 10s whose gnomon 

 must make an angle with the plane of the dial, equal to 

 the co-latitude of the place ; and the hours must be set 

 the contrary way on this dial, to what they are on the 

 horizontal. 



But if your globe have more than 24 meridian semi- 

 circles upon it, you must take the following method for 

 making horizontal and south dials. 



To con- Elevate the pole to the latitude of your place, and 

 tract & ho- t urn the globe until any particular meridian (suppose 



nzontai J l 



dial. the first) comes to the north point of the horizon, and 

 the opposite meridian will cut the horizon in the south. 

 Then, set the hour-index to the uppermost XII on its cir- 

 cle ; which done, turn the globe westward until 15 de- 

 grees of the equator pass under the brazen meridian, 

 and then the hour-index will be at 1, (for the sun moves 

 15 degrees every hour) and the first meridian will cut 

 the horizon in the number of degrees from the north 

 point, that I is distant from XII. Turn on, until other 

 15 degrees of the equator pass under the brazen me- 

 ridian, and the hour-index will then be at II, and the 

 first meridian will cut the horizon in the number of de- 



Note 104. If the latitude be subtracted from 90 degrees, the re- 

 mainder is called the co-latitude, or complement of the latitude. Note 

 by the Author. 



Note 105. For if the plane of ike horizon to the globe be placed in 

 a vertical position, anJ directly facing the south, the axis ol the globe 

 will be parallel to the axis of the earth. 



