178 Professor C. Piazzi Smyth's Meteorological 



the line of axis will perform a complete revolution from this 

 cause in 30 hours nearly. Also that if a common seconds 

 pendulum (which performs its double vibration in 2 seconds) 

 vibrates in an ellipse whose major axis is 4 inches and minor 

 axis T^th inch, the line of axis will perform a complete re- 

 volution /ro/w this cause in 30 hours nearly. The direction 

 of rotation of the line of the axis, being the same as the 

 direction of revolution in the ellipse. He likewise shews that 

 errors in the point or mode of suspension, or the wire passing 

 through a somewhat oval hole, or being unequally shaped on 

 different sides, may cause an apparent vQwo\\xi\on of the plane of 

 vibration ; though this may be eliminated by making two sets 

 of experiments and changing the commencing azimuth by 45°. 



These numbers and facts should be laid to heart by all 

 who undertake to exhibit the rotation of the earth, and they 

 should not presume to say that this residual quantity has 

 been revealed, until they have corrected their apparatus for 

 such innate and necessary imperfections as produce results so 

 similar in appearance to those which they are in search of. 



The Total Eclipse of the Sun on July 28. — In our January 

 number, we drew attention to this important phenomenon, 

 and since then a pamphlet of " suggestions"* for its due 

 observance, has emanated from a Committee of the British 

 Association appointed for that purpose. The importance of 

 the pamphlet is greatly increased by an accurate and detailed 

 map of the path of the shadow over Europe, giving a con- 

 densed view of the careful and exact series of extensive cal- 

 culations, which the Astronomer Royal, one of the members 

 of the Committee, recently had performed at Greenwich. As 

 he gave a popular lecture recently at the Royal Institution, 

 on the nature of and the importance of observing this phe- 

 nomenon, and something of the same sort is contemplated 

 during the meeting of the British Association at Ipswich, 

 in the first week of next month, it is to be hoped that a 

 goodly array of competent observers will be distributed along 

 the line of the eclipse, so as to ensure in so cloudy a region 

 as Europe ; some good and efficient observations being ob- 



* The *' Suggestions,^^ and an abstract of the Astronomer Koyal's Z/ecfwre, deli- 

 vered in the Royal Institution, are given in the preceding pages of this Number. 



