38 REPORT 1855. 



W. Richards has kept a register) of any size have ever fallen except once, and then 

 they were only 2^ inches in circumference. The stones measured from 1 to 14 

 inches about. 



TV/iai is a Hailstorm''. — Aqueous vapour condensed into ice, by passing through 

 an intensely cold atmosphere, is the apparent, and probably the true answer. Some 

 contend, that, because hail falls so rarely in winter, and the cloud whence it comes 

 is usually at no great altitude, there being at the same time almost always thunder 

 and lightning (with atmospheric electrometers changing in intensity), and passing 

 from positive to negative, and vice versa (ten times in a minute), hence electricity 

 must have quite as much to do in the matter as cold. But the latter seems the most 

 reasonable view. In almost all very large hailstones (as was observed here) is found 

 a nucleus, a piece of snow, or a small opake hailstone in the centre, surrounded by 

 transparent coverings, one over another, concentrically arranged (like an onion), 

 leading to the belief that the first concretion was a small one, and that it accumulated 

 in its descent ; that a whirlwind above kept battering these formations together, and 

 prevented their falling, until at length, immensely enlarged, and getting out of this 

 influence, they came down upon terra firma. We are not justified in assigning limits 

 to the amount of cold in the upper strata of the atmosphere. 



On a Rainbow seen after Sunset. By the Rev. Professor Chevallier. 



At the meeting of the Association in 1849, an account was given of a rainbow 

 seen after actual sunset (Report, p. 16) ; and it was suggested that, in order to 

 account for it, either the horizontal refraction must have been much greater than its 

 ordinary value, or the rainbow must have been formed in a very elevated region of 

 the atmosphere. 



On August 11, 1855, a rainbow was seen at Whitby, by Mr. C. P. Knight, 

 which seems to show that such a phsenomenon may arise from rain falling at a 

 great height. The mean Greenwich time of the apparent setting of the sun's upper 

 limb, taking refraction into account, was 7^ 44™. 



At 7*^ 30™, " railway time," a rainbow was seen, and continued to be visible till 

 7'' 48™, which is thus described. "It appeared to be far above the earth's surface. 

 It was higher up than some clouds called cirro-stratus (in a sketch which accom- 

 panied the account) ; and those clouds were seen in front of the bow in several 

 places. Rain-clouds were some distance below these, and far above all were some 

 filmy light cirri, lit up by the sun. There were only two or three small spaces of 

 blue sky to be seen. No rain had fallen for some hours ; and there was no appear- 

 ance of any falling where the bow was. The time I had was Greenwich time." 



Although the time given may not be quite accurate, it seems to be established 

 that this rainbow was seen after actual sunset, and that it was formed in an elevated 

 region of the atmosphere. 



Improvements on a Dew-point Hygrometer lately described by the Author. 

 By Professor Coxnell, F.R.S. L. <§• E. 



This instrument consists of a little bottle of thin brass, polished externally, con- 

 nected laterally with a small exhausting syringe, and having a thermometer inserted 

 in it, by means of an air-tight brass stopper. Ether having been previously intro- 

 duced into the bottle, the temperature is gradually reduced by working the syringe 

 until moisture is deposited on the bottle. The thermometer then indicates the dew- 

 point. An intercepting portion of ivory prevents the communication of the heat of 

 friction to the bottle. The valves of the syringe are constructed of gold-beaters' leaf. 



A few simple changes, since the instrument was described in the Transactions of 

 the Royal Society of Edinburgh and in the Philosophical Magazine for 1854, have 

 greatly facilitated its manipulation, and have made it less liable to injury. 



The brass bottle is now connected with the syringe by means of a coupling screw 

 instead of a common screw. This permits the bottle with the inserted thermometer 

 to be at once brought into the proper vertical position, whatever be the nature and 

 situation of the fixture to which the clamp, by which the instrument is secured when 

 in operation, is attached. The projecting portion of the ivory intercepting partition 

 is now made of brass, and is therefore not liable to fracture as it was previously. 

 The form of the key employed in screwing and unscrewing the parts of the instru- 



