COMPARATIVE METEOROLOGICAL OBSERVATIONS. 231 



a subject of careful study, and the effect of direct sunlight was of course 

 omitled. Eecords were also made upon the barometer, direction and 

 force of winds, cloudiness, movement of clouds, and notices of rain, snow, 

 and its lodgment in branches, fog, dew, hoar- frost, ice, &c. 



The following are the instructions upon placing and observing the in- 

 struments which would be of service in the establishment of similar 

 stations, and would tend to secure comparability of result : 



Of the conditions of the place u'here oiseirations slwuld he made. — These should be made 

 in a large forest, and in an open tract adjoining. They should be gradually extended 

 to different kinds of deciduous and evergreen forests, and to dense woods with the 

 ground covered and uncovered with litter, with the trees so close together as to wholly 

 shade the ground, and to places where the light comes in between the branches. They 

 should also include dwarf-woods, where the ground is bare and hard from the contin- 

 ued removal of litter — woods in which a bed of moss has formed over the surface, and 

 in different aspects and soils. 



The unwooded place for the accompanying observations should be entirely free from 

 hills or other eminences, and of sufficient size to be free from the influence of a neigh- 

 boring woodland, either by shading, cooling, or obstructing the winds. Yet the two 

 places should not be far distant from each other, and in surface and soil as nearly alike 

 as possible. A description should be made as regards elevation above sea-level, condi- 

 tion of soil, aspect, slope, and surroundings. For protection against accident or inter- 

 ference, the places of observation should be fenced in. 



Of the putting up and management of instruments and the maJcing of observations. — The 

 instruments should be put up by experts, duly appointed. They must be handled 

 carefully, and so as to prevent injury. The places of observation are never to be 

 changed without the written consent of the director of forest stations. Should au 

 instrument be injured, written notice is immediately given to the director, who will 

 replace it. The following rul#s for observation are to be followed: 



1. The SELF-KEGrsTERiNG THERMOMETER (thermometrograph), in thinly-wooded for- 

 ests and in open fields, must be protected from the direct or reflected rays of the sun by 

 a wooden screen, and a small roof of wood, covered with zinc, should be placed over it 

 to keep ofl:' the rain. It should be fixed upon a post, five feet above the ground, and 

 should be perfectly horizontal. After each reading it is adjusted by holdiug it slant- 

 ing, and by gently jarring, till the indicator, by its own weight, falls back upon the 

 mercurial column, and the little glass bar touches the end of the spirit-column. The 

 minus sign ( — ) should be placed before figures read below zero. 



2. The psychkometer consists of two thermometers by Lamont, and graduated to 

 degrees and tenths (R). The pressure of vapor, in Paris lines, is determined by the 

 readings of wet and dry bulb instruments, and by the aid of tables. Ouly the difference 

 between them need be entered. The covered bulb is moistened by dipping in a cup of 

 rain or snow water about a minute before reading. Care should be taken that no drop of 

 water remainson. In winter, when this bulb is covered with ice, wetting is unnecessary. 

 In summer, repeated dippings are often required, as the water does not adhere freelyi 

 If the dry bulb has become wet, or is covered with frost, it must be carefully wiped 

 dry about ten minutes before observation, which should never be made until it has 

 returned to the temperature of the air. In reading, the eye of the observer should be 

 level with the point read, taking care not to aliect the instrnmeut by bringing the 

 face too near or by breath or touch. This instrument is put uj) on the same frame with 

 the self-registering thermometer, and under the same roof. 



3. Rain and snow gauges. — The rain-gauge, by differences of record, should show 

 the amount of water intercepted by the leaves and branches. In the woods, the 

 instrument should be in a place where the trees are so close that their branches inter- 

 lace, as they average, and in the open fields, so that no rain may be driven in from 

 roofs or other objects. The receiving-surface has an area of one square foot. It should 

 be level, and about 8 feet above the ground. Snow, hail, and sleet, are to be measured 

 in a melted state, and a spare receiver of equal size is used while the other is removed 

 for melting the contents. In case of heavy falls of snow, the contents may V>e pressed 

 down, and when full another should be jilaced. The water is drawn off into a glass 

 cylinder graduated into Paris cubic inches and lines, and measured. Its actual amount 

 must be recorded, and not the height at which it stood in the cylinder. After each 

 reading the glass cylinder should be carefully wiped with a linen cloth. The metallic 

 vessels are also to be kej^t clean. To avoid too low estimates, extra measurements 

 should be made in cases of heavy falls of rain or snow. 



To find the amount of water lost by evaporation, running off, or soaking into the 

 ground and draining away, in fields and woodlands, zinc ve^-sels, 1 Paris foot square 

 at the top and 1,2, 3, and 4 feet deep, are provided, with a double bottom, the upper one 

 of which is perforated, andfastened about four inches above the lower one, as shown at 



