ECLIPSES. 



28. Solar eclipse of 1851. 29. Observations of the Astronomer 

 Royal upon it. 30. Observations of Messrs. Dunkin and Humphreys 

 upon it. 31. Observations of Mr. W. Gray upon it. 32. Ob- 

 servations of Messrs. Stephenson and Andrews at Fredrichsvaarn. 

 33. Observations of Mr. Lassell at Trollhattan Falls. 34. 

 Observations of Mr. IJind at Ravelsborg, near Engelholm. 



1. OF the objects which in such countless numbers are scattered 

 over the firmament, all those which constitute the solar system, 

 except the sun itself, are in motion; and it must necessarily 

 happen, occasionally, that some of them will assume a position 

 between others and the eye of the observer placed upon the 

 earth. When such an event happens the nearer of the two will 

 intercept wholly or partially the view of the more distant. If 

 the apparent magnitude of the nearer be greater than the more 

 distant, such an obstruction may be total, but if less it can only 

 be partial. 



2. Since all the bodies of the solar system are illuminated by 

 the sun, and when deprived of the sun's light are obscured and 

 cease to be visible, it may also happen that some on e of the bodies 

 composing the system may intervene between the sun and another 

 body, so as to deprive the latter of the light which it receives 

 from that luminary. In such a case the object deprived of light 

 will be rendered wholly or partially invisible, according to the 

 relative magnitude of the two bodies, the one intercepting the 

 light and the other being obscured. 



3. Such conjunctions produce a class of occasional astronomical 

 phenomena, which are invested with a high popular as well as a 

 profound scientific interest. The rareness with which some of 

 them are presented, their sudden and, to the vulgar mass, un- 

 expected appearance, and the singular phenomena which often 

 attend them, strike the popular mind with awe and terror. To 

 the astronomer, geographer, and navigator, they subserve im- 

 portant uses, among which the determination of terrestrial 

 longitudes, the more exact estimation of the sun's distance 

 from the earth (which is the standard and modulus of all dis- 

 tances in the celestial spaces), and, in fine, the discovery of 

 the mobility of light, and the measure of its velocity, hold 

 foremost places. 



The phenomena resulting from such contingencies of position 

 and direction are variously denominated ECLIPSES, TKA^SITS, and 

 OCCTJLTATIONS, according to the relative apparent magnitudes of 

 the interposing and obscured bodies, and according to the circum- 

 stances which attend them. 



4. When the disc of the moon passes between an observer and 

 the disc of the sun, it intercepts in this manner more or less 



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