Curiosities of Science. 77 



were less by 55 45' than at present. Calculating from this datum 

 the place of the pole of the heavens among the stars, it will be found 

 to fall near a Draconis ; its distance from that star being 3 44' 25". 

 This being the roost conspicuous star in the immediate neighbourhood, 

 was therefore the Pole Star of that epoch. The latitude of Gizeh being 

 just 30 north, and consequently the altitude of the North Pole there 

 also 30, it follows that the star in question must have had at its 

 lowest culmination at Gizeh an altitude of 25 15' 35". Now it is a 

 remarkable fact, that of the nine pyramids still existing at Gizeh, six 

 (including all the largest) have the narrow passages by which alone they 

 can be entered (all which open out on the northern faces of their re- 

 spective pyramids) inclined to the horizon downwards at angles the 

 mean of which is 26 47'. At the bottom of every one of these passages, 

 therefore, the Pole Star must have been visible at its lower culmination ; 

 a circumstance which can hardly be supposed to have been uninten- 

 tional, and was doubtless connected (perhaps superstitiously) with the 

 astronomical observations of that star, of whose proximity to the pole 

 at the epoch of the erection of these wonderful structures we are thus 

 furnished with a monumental record of the most imperishable nature. 



THE PLEIADES. 



The Pleiades prove that, several thousand years ago even 

 as now, stars of the seventh magnitude were invisible to the 

 naked eye of average visual power. The group consists of 

 seven stars, of which six only, of the third, fourth, and fifth 

 magnitudes, could be readily distinguished. Of these Ovid 

 says (Fast. iv. 170) : 



" Quae septem dici, sex tamen esse solent." 

 Aratus states there were only six stars visible in the Pleiades. 



One of the daughters of Atlas, Merope, the only one who 

 was wedded to a mortal, was said to have veiled herself for 

 very shame and to have disappeared. This is probably the 

 star of the seventh magnitude, which we call Celaene ; for Hip- 

 parchus, in. his commentary on Aratus, observes that on clear 

 moonless nights seven stars may actually be seen. 



The Pleiades were doubtless known to the rudest nations 

 from the earliest times ; they are also called the mariner's stars. 

 The name is from TrAeiv (plein), ' to sail.' The navigation of 

 the Mediterranean lasted from May to the beginning of Novem- 

 ber, from the early rising to the early setting of the Pleiades. 

 In how many beautiful effusions of poetry and sentiment has 

 " the Lost Pleiad" been deplored ! and, to descend to more fa- 

 miliar illustration of this group, the " Seven Stars," the sailors' 

 favourites, and a frequent river-side public-house sign, may be 

 traced to the Pleiades. 



CHANGE OF COLOUR IN THE STARS. 



The scintillation or twinkling of the stars is accompanied 

 by variations of colour, which have been remarked from a very 

 early age. M. Arago states, upon the authority of M. Babinet, 



