Mr H. Meikle on Compensation Pendulums, 387 



thought had till then been overlooked. As, for instance, the 

 defects of various compensations arising from the different 

 parts of a pendulum not being all at the same temperature, 

 and, in particular, the imperfections of the mercurial pendu- 

 lum on this account. But whoever will take the trouble of 

 looking into the article Pendulum of the Encyclopaedia Britan- 

 nica, will find that such ideas are by no means so new ; be- 

 cause I had there pointed out the same things, and they were 

 published more than four years before the illustrious astro- 

 nomer of Konigsberg took up the subject. 



There is, however, I suspect, another defect in the mercu- 

 rial pendulum ; and which, so far as I am aware, has not yet 

 been attended to. The performance of that pendulum is al- 

 ways assumed to be exactly the same as if the mercury in it 

 were a perfectly rigid mass. But, since mercury is allowed 

 to be one of the most perfect of fluids, there can be no doubt, 

 that, when the pendulum is in motion, the surface of the mer- 

 cury, which is of considerable extent, must be in a state of 

 perpetual undulation. The precise amount and effect of this, 

 it will be no easy matter to determine ; but there is reason 

 to think that it must tend to retard the pendulum, and to 

 add to the inequality of the times of the greater and less vi- 

 brations. One way of nearly obviating it would be to use a 

 less mass of mercury, and put it in a bottle with a narrow 

 neck, the upper surface of the mercury being half way up 

 the neck. But this would not necessarily do anything towards 

 giving the same temperature to the whole pendulum rod, or 

 the mean temperature to the compensation, unless the centre 

 of gi^avity of the mass of mercury were near the middle of 

 the rod. In that form, however, the mercury could not con- 

 veniently serve as the principal mass of the pendulum. 



Analysis of the American Mineral Nemalite. By Arthur 

 CONNELL, Esq., F.R.S.E., Professor of Chemistry, Univer- 

 sity of St Andrews. Communicated by the Author. 



This mineral bears a striking resemblance to asbestus, so 

 that by the eye it can hardly be distinguished from it. It 



