268 



NA TURE 



\_yan. 20, 1 88 1 



anthracite, ought not to rejoice in a pure and transparent 

 atmosphere. . 



Similarly, the South Wales coal and iron districts would be 

 centres of fog clouds and mist, like Birmingham and Newcastle. 

 But they are as free from fog as the 'purely pastoral valleys of 

 Wales. 



Next, as to persistency. Early in the morning of January 31 

 last, in some districts of London the fog extended considerably 

 above the tops of the houses, in others only about 10 or 20 feet 

 from the ground in any intensity. Where the fog extended high 

 the smoke mixed with it and produced a yellow fog, but where 

 it remained low the smoke escaped into the upper air and drifted 

 away, leaving a white fog below, so pure as to be a very unusual 

 phenomenon at 10 a.m. in a London street. Now it was remark- 

 able, that wherever the white fog prevailed in the morning, the 

 sun soon obtained the mistery and dispelled it more or less, but 

 in the smoke-obscured districts a dark yellow fog continued 

 throughout the day. 



White fogs may doubtless be exceedingly dense. But will not 

 an admixture of smoke increase its density ? 



A humid atmosphere is not necessary for the production of 

 mist and haze. I'he frequent long-continued prevalence of blue 

 haze over the whole country, not excepting the east coasts, in the 

 driest east winds of spring, would be a subject deserving investi 

 gation. They sometimes extend to a height much above llie 

 top^ of our highest mountains. Experiments such as tho e of 

 Mr. Aitken will, we may hope, ultimately solve this proMeai r.f 

 meteorology. I^' Russell 



Low Temperature 



THEi-eadingof the thermometer here last night, January 15, 16, 

 was the lowest ever recorded at this o' iservatory in the conr^e of 

 thirty-three years. The reading was 4°'6 F., the previous 

 minimum having occurred on December 24, i860, when the 

 mercury stood at 6°7 F. S. J. Pekrv 



Stonyhurst Observatory, January 16 



A "Natural" Experiment in Polarised Light 

 Break off a plate of ice and hold it between the sky and a 

 pool of water. Its reflected image will show the beautiful 

 colours due to polarised light. The incident rays should come 

 from a part of the sky about 90° from the sun, and reflection 

 should take place at the polarising angle for water, and the plate 

 will probal.ly require adju-ting to bring out the maximum elTcct. 

 Water, vaporous, solid, and liquid, thus furnishes us with pobri-er, 

 crystal, and analyser I do not remember to have read any 

 account of this very simple experiment, for which Nature provides 

 aU the materials. Chas. T. Whitmell 



9, Beech Grove, Harrogate, January 10 



STATICS AND DYNAMICS OF SKATING 



MANY years ago, when skating was but in its infancy, 

 skates were made of bone, and if they could be 

 made to stay on the feet they were considered to answer 

 their purpose sufficiently well. 



More recently iron runners with wooden beds came into 

 use, and accuracy of adjustment on the foot, horizontally 

 and longitudinally, was made easier by means of leather 

 straps and a screw passing into the heel of the boot ; and 

 these adjustment:-, made haphazard, were quite sufficient 

 for the skating of those days, namely forward skatmg. 



Within the last twenty years however skating has made 

 enormous strides, back skating becoming an essential 

 qualification of a finished s';ater ; and hence not only 

 more perfect forms of s':ate are demanded from the 

 maker, but also the adju^tment of them on the boot be- 

 comes an important part of his duty. 



There are tliree points to be attended to in the adjust- 

 ment of the s'-.ate, besides the obvious one of placing the 

 skate medially on the foot. 



1. Height of foot off the ice where the greatest breadth 

 of the sole of boot occurs. 



2. Height of foot off ice at the heel. 



3. Posiiion of the skate longitudinally or lengthwise 

 on the foot. 



First. The height of the foot from the ice should be 

 such as will enable the skater to lean over sufficiently 

 when on a curve, and such that he may be able to get a 

 powerful enough stroke. If he is too low the edge of the 

 boot will come in contact with the ice in leaning overt 

 and also in taking a stroke ; a fall ensuing in the firs, 

 case, and a disagreeable and dangerous overstrain in the 

 second. To avoid these the sole of the boot should sub- 

 tend an angle at the bottom of the runner of about 96 

 deg. i.e. for a sole 3i inches broad the edge of the runner 

 should be i^ inch from the sole, instead of varying from 

 1 1 to I ^ mih, which are the heights of skates commonly 

 met with. 



This angle of 96 deg. will be found to clear the ice in 

 both striking and leaning over for most skaters, and any 

 greater height than is given by this angle should not be 

 used, as it is not necessary, and only throws an additional 

 strain on the ankle. 



Second. The height at the sole having been fixed, the 

 next point is what should be the height at the heel ? In 

 fact is the foot to be parallel to the skate, or is it to rest 

 on an incline ? 



Dove was the first person, in his " Skater's Monitor," 

 published in Edinburgh in 1846, to write on the position 

 of the skate on the foot, summing up his remarks by 

 saying, " Level woods then are for shoes whose heels 



Fi^.Z. 



and soles are equally prominent, but high heels must be 

 sunk into the skate-woods." This was quite correct at 

 that lime, when back skating was little practised, and 

 when the skate which was then worn was made very flat, 

 in fact almost straight at and near the heel. Now, by 

 universal consent for figure-skating, the iron is made a 

 segment of a single circle from toe to heel, 7i feet 

 being the radius. Yet, notwithstanding these changes, 

 Vandervell and Witham, as lately as January, 1880, in 

 their " Figure Skating," recommend the very same 

 parallelism of the foot to the skate instead of parallelism 

 of the top of the blade to the ice, as it should be for 

 modern skating, as I shall subsequently show. 



In Fig. I is shown the result of adopting Dove's or 

 Vandervell and Witham's position, i.e. no heel. It 

 might be thought that a person standing on a curve 

 would balance comfortably at the middle of the curve, 

 but this cannot be, for a person standing naturally on a 

 level surface does not distribute the weight of his body 

 equally over the length of his foot, but by far the greater 

 part comes on the heel, and therefore the centre of pres- 

 sure of his body is nearer the heel than the toe, and con- 

 sequently if he'is standing on a curve the curve must roll 

 up in front and down behind till the upward pressure of 

 the ice just passes through the centre of pressure of his 

 body. The point of contact of the skate on the ice will 

 therefore not only be much behind the centre of the 

 skate, but will be a little behind the centre of pressure of 

 his body when standing on a level surface, as he now 



