232 



KNOWLEDGE. 



[OOTOBEB 2, 1899. 



hour's observation is set down for the whole day. On the 

 second hne each hour's observation is again set down 

 for the second day of the month, and for the thirty-one 

 days of the month. In addition to the twenty-four 

 records, the sums and means, and maxima and minima 

 are also recorded in each line, then at the end of the 

 month each of these columns is added up vertically and 

 meaned. Thus at the foot of the page is the series of 

 means for the same hour for every day during the 

 whole month, and in the last vertical column are all 

 the means for the whole day every day of the month. 

 The mean for the whole month is obtained by taking 

 the mean of either of these columns — namely the vertical 

 or horizontal one ; and by working both, there is an 

 effective check upon any arithmetical or clerical error, 

 which not unfrequently occurs, and often involves a great 

 deal of labour to find out. By this means not only are 

 the observations made, but are tabulated and prepared 

 for further discussion. 



As long as the weather is fine all this work is straight- 

 forward enough, but fine weather, it may be said, is 

 exceptional on Ben Nevis. It has been said that in summer 

 the climate of Ben Nevis may be regarded as much the 

 same as that of Spitzbergen. I have spent the summer in 

 Spitzbergen as well as on the summit of Ben Nevis, and I 

 should say that there is more fine weather during that 

 period in Spitzbergen than on our Ben. As for the rest of 

 the year the weather on Ben Nevis is far from pleasant, 

 and during bad weather the work of observing is not to be 

 envied. The usual rule is that every hour the man on 

 duty has to put on his oilskins and sea boots and face 

 pelting rain or driving snow, and find his way through 

 thick mist or fog to the thermometer screens, rain gauge, 

 and other instruments, stationed some way from the house 

 in order that they may not be affected by it in any way ; 

 all the night long he has to take out a lamp every hour, 

 and if the wind is high the lamp may blow out. This 

 frequently happens, in spite of very carefully constructed 

 lamps, in which case he has to grope his way back to the 

 house in the dark, and woe betide him if he go in the 

 wrong direction, for close to the Observatory is the Great 

 Chff, which is sheer up and down for nearly two thousand 

 feet ! Digging and clearing the snow from the lower 

 windows and door is, as I have said, another duty of the 

 observers, although "for days at a time digging is rendered 

 useless by the continual drifting of the snow"; then 

 paraffin lamps have to be burnt by day as well as by night. 

 During such weather as this the observers have to go 

 out oftener than usual. Thermometer screens have to be 

 cleared of drifted snow which chokes up their louvres, and 

 thus prevents a clear circulation of air round the instru- 

 ments. What is even worse, the fog throws an accre- 

 tion of ice crystals upon everything; then the instru- 

 ments are blocked up even more than by driving snow. 

 Worse than fog crystals or snow, however, is when the 

 condition known as " silver thaw" prevails, that is, rain 

 falling when the air is below the freezing point and 

 freezing as it falls, covering every object with a clear hard 

 layer of ice. Especially on the latter occasions, as well 

 as when fog crystals are forming and snow drifting, have 

 the thermometer screens to be cleared, and when they get 

 hopelessly blocked up, they simply have to be brought — 

 screen, instruments and all — into the house to be thawed, 

 and a new set put out. This is more easOy effected 'oy a 

 special movable box, which is always used during the 

 winter months, and is lashed on to a ladder-like stand. 

 Besides being a useful arrangement for allowing the 

 screens to be brought into the house to get cleared, it is 

 also useful for changing the height of the box. iShade 



temperature observations should always be taken at a 

 height of about four feet from the ground, and by this 

 arrangement, as the winter snow increases in depth, the 

 Stevenson screen can be raised accordingly, so that it shall 

 always be the normal height above the surface of the 

 ground, for the surface of the snow must be regarded as 

 the surface of the ground during winter. " The vital 

 importance of thermometric observations is emphasised by 

 the circumstance that without them the barometric obser- 

 vations are of comparatively small value, no approximation 

 to a knowledge of the temperature of the air-stratum 

 between high and low level observatories being possible. 

 Ben Nevis is the only observatory that has hitherto coped 

 successfully with this all-important department of the 

 work of a high-level observatory, and one cannot suffi- 

 ciently admire the heroic endurance with which the 

 observers have made the hourly observations by night and 

 by day, in all seasons, these years past." 



^ 



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Fig. 4. — Fog CrjstaU covering Tower and Instruments ; Winter. 



In addition to the ordinary routine work of a " first-order 

 meteorological observatory " a great deal of extra research 

 work has been accomplished by volunteers and by members 

 of the staff. Messrs. Omond and Rankin have made an 

 exhaustive examination of the winds of Ben Nevis, which 

 has been published in the Transactions of the Royal Society 

 of Kdinhurgh. It is found that the Ben Nevis winds do 

 not agree with the distribution of barometric pressure at 

 sea level according to Buys Ballot's law of the winds 

 in relation to pressure, but point to a widely different 

 distribution of pressure at four thousand four hundred 

 and seven feet as compared with the distribution at 

 sea level. The effect of high winds on the height of 

 the barometer is another of Dr. Buchan's investigations. 

 In forecasting weather it is necessary to keep this effect 

 constantly in mind, " with the view of arriving at a 



