148 Instructions Jbr Making and Registering 



the most distant stations, if duly OLVserved by persons furnished with means 

 of ascertaining the time. 



Thunder-storms of course will be noticed when they occur under the gene- 

 ral head of the weather, but it is of consequence also to notice distant light- 

 ning, not accompanied with thunder audible at the place of observation (by 

 reason of its great distance), * especially if it takes j)lace many days in suc- 

 cession, and to note the quarter of the horizon where it appears, and the 

 extent it embraces. In an actual thunder-storm, especial notice should be 

 taken of the quantity of rain that falls, and of the fits or intermittances of 

 its fall, as corresponding, or not, to great bursts of lightning, as also of 

 the direction of the wind and the apparent progress of the storm with or 

 against it. 



Observations of the Electrical state of the Air in serene weather are un- 

 fortunately too much neglected. The apparatus they require is simple, and 

 by no means costly, and may be constructed indeed by any one for himself 

 with ease. 



If the Committee in this their first Report do not dilate on this and other 

 of the less usually practised observations of Meteorology, it is because they 

 wish for the present chiefly to call attention to the accumulation of re- 

 gular and daily observations of a more definite and numerical character. With 

 this view they have drawn up, and by the liberal aid of Government, have 

 procured to be printed skeleton forms, of which a copy is annexed, for im- 

 mediate distribution among such Correspondents of the Institution, and others, 

 as may be willing to undertake their filling up. These comprise, it is true, 

 only the registers of the Barometer and its attached Thermometer, with 

 that of the external Thermometer, and a column of Remarks for Wind and 

 Weather, as being the most essential and indispensable elements of Meteoro- 

 logy ; but it is in the power of any one who pleases to supply additional infor- 

 mation, and to those who have leisure, instruments, and inclination for the 

 task, the Committee would particularly recommend the regular observation of 

 the Wet Thermometer, those of the SeU-registering Thermometer and Weekly 

 or Monthly Observations of Thermometers buried at different and progressive 

 depths beneath the surface of the soil. 



The printed forms provide for the arithmetical convenience of casting up 

 the means for each month. In doing so, it is requested that care will be taken 

 to verify the results by repetition, and (that usual sources of error may not 

 escape notice) they recommend in every instance, before adding up the 

 columns, to look down each to see that no obvious error of entry (as of an 

 inch in the barometer, a very common error, or what is more difficult of de- 

 tection, an error in the first decimal place) shall remain to vitiate the mean 

 result. It is perhaps unnecessary to do more than mention the precaution of 

 counting the days in each column on which observations occur, so as to admit 

 of no mistake in the divisor^ and to use throughout the decimal arithmetic in 

 calculating the mean ^results. Care and exactness in these points will in 



* Thunder can scarcely ever be heard more than 20 or 30 miles from the flash 

 which produces it. Lightning, on the other hand, may be seen (or at least its re- 

 flexion on the clouds, forming what is called sheet lightnimf) at the distance of 150 or 

 200 miles. 



