ON SEISMOLOGICAL INVESTIGATION. 141 



which has accumulated is roughly rolled up. At this time the date may 

 be written in pencil on the bromide film on the top of the upper roll. 

 The small top roll shown in the sketch should barely touch its neighbour, 

 whilst a corresponding roll in contact with the driving-roll should press 

 somewhat tightly on the latter. These two latter rolls are not shown in 

 the sketch. Should the papers at any time refuse to move freely, it may 

 be necessary to alter the adjustment between these rolls to see that they 

 have not become sticky by contact with the bromide surface, or even to 

 cover the driving-roll with a piece of thin but roughish paper. If 

 moisture is suspected as being the cause of a stickiness of the bromide a 

 saucer of calcium chloride may be placed in the clock-box. The most 

 convenient form in which to use this substance is as cake mixed with 

 asbestos. Every week this can be dried over a strong fire. 



Calcium chloride, or other desiccating agents, must not be introduced in 

 the instrument-case, for if they are a circulation of air is set up, and the 

 boom swings to and fro, giving records which have often been called earth- 

 tremors. For earthquake work the driving-roll must be adjusted in its 

 outermost position, when it will turn once per hour. In its inner position 

 it turns once in twelve hours, when it may be used, for example, for studying 

 the diurnal wave. 



The Watch. — This must be compared fairly often with a standard 

 timekeeper, and its rate noted. It is particularly important that the 

 time at which its hour-hand commences and ends its eclipse over the slit 

 in the clock-box be noted, as it is from these markings that the times of 

 earth disturbances are measured. This can be done either by watching 

 the hour-hand of the watch by looking down the tube down which the 

 mirror reflects light, or by watching the same when the clock-box is taken 

 out of the instrument-case. 



Developing, fixing, and copying the Film. — The films, which are 25 feet 

 in length, are developed once a week. The developer employed has been 

 chosen, because the same solutions may be used for several successive 

 developments. The stock is kept as two separate solutions, made up as 

 follows : — 



1st Solution. 



' Sulphate of soda, I oz. or 1 part by weight. 



Carbonate of potash, ^ oz. or \ ,, „ ,, 



Bromide of potash, Jg oz. (lOgrs.) or;^ „ „ „ 



Water, 5 oz. or 6 „ „ „ 



2nd Solution. I^f.''^' I T' ^^^ ^''-^ °' I " " " 



(^ Water, 5 oz. or 5 „ „ „ 



For use one ounce of each of these solutions is to be taken and mixed 

 with about 24 ounces of water, and the whole is then poured into the 

 developing- tray. 



The film is doubled backwards and forwards in this solution, and the 

 tray kept agitated until the development takes place, when the solution 

 is poured off into a bottle to be kept until the following week. After the 

 second time of use it may be strengthened with half an ounce of each of 

 the above two solutions, when it will last two weeks longer. It is then 

 thrown away. The next operation is to pour water once or twice into the 

 developing-tray, and to rinse the film, after which it is dragged bodily over 

 the end of the tray into a second tray containing a strong solution of 

 hyposulphite of soda (1 hypo and about 4 water). Whilst in this solu- 

 tion the folds of the film are one by one gently opened to allow the hypo 



