10 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



Laplace selected Brest, where the tide has a direct and 

 short approach from deep water, and, neglecting the effect of 

 friction referred to, obtained, as is well known, the value of 

 ^thj, in terms of the earth's mass, for the mass of the moon. 

 At Brest the ratio of the half-monthly inequality to the co- 

 efficient or half range of the constant tide is about .358, that 

 of the constant tide being about 2.25 metres, and that of the 

 mean spring-tides about 3.05 metres. At Boston the same 

 ratio is only about .14, the co-efficient of the constant tide 

 being 4.91 feet, and that of the mean spring-tides 5.58. From 

 data so widely different Mr. Ferrel has deduced, by means of 

 the introduction of the term depending upon friction, two 

 values exhibiting a remarkable agreement, viz., from the Brest 

 tides y^-re, and from those at Boston y^Vr- &" Nat. Acad. 

 (unpublished). 



PARALLAX OF A STAR. 



The bright star a Lyrae must now be added to the few of 

 which the parallax is known with considerable accuracy. Dr. 

 Brunnow, formerly director, of the observatory at Ann Arbor, 

 and now astronomer royal for Ireland, has lately computed a 

 series of careful and most accurate measurements on this star, 

 made by comparison with a minute star near it, known as 

 Struve's Companion. The result is that the parallax is- al- 

 most exactly one fifth of a second. An idea of the smallness 

 of this angle may be formed by reflecting that the smallest 

 visible object subtends an angle of about one minute; so 

 that if the angle which Dr. Brunnow had to measure were in- 

 creased three hundred times, it would still appear to the 

 naked eye as a mere point. Yet this is the angle subtended by 

 the distance from the earth to the sun as seen from the star. 

 The corresponding distance of the star is a little more than 

 a million times that of the sun, or about 93,000,000,000,000 

 miles. Previous determinations of this parallax, by Peters 

 and the Struves, have ranged from one tenth to one fourth of 

 a second ; but the extreme difficulty of measuring so small 

 an angle made them all a little doubtful. (Communicated.) 



IS THE AURORA VISIBLE IX DAYLIGHT? 



The question whether the aurora is visible by daylight, as 

 propounded some time ago in Nature, has met with several 



