660 Professor George ChrysUd [May 17, 



system of multiplying leyers, working the pen which writes on the 

 recording drum. The inertia of the working parts is yery small, 

 and the sensitiyeness to alteration of pressure is 15 or 20 times that 

 of an ordinary mercury barometer. The instrument will therefore 

 show quite plainly extremely small deniyellations of the lake ; and it 

 can be made more or less sensitiye by increasing or diminishing the 

 diameter of the well. By merely turning the stopcock, and shutting 

 off the communication with the well, we conyert the instrument into a 

 yery sensitiye barometer. The curye which it traces is thus changed, 

 at a moment's notice, from a limnogram into a barogram, so that we 

 can alternately record the deniyellation of the lake and the yariation 

 of the atmospheric pressure. I shall show you some of the results 

 obtained later on. The instrument itself I call a statolimno- 

 graph. 



In addition to the statolimnograph, and four index limnographs 

 which were worked at constantly yarying points, we had three fixed 

 limnographs, one near St. Fillans, one near the binode, and one near 

 the uninode. The last, unfortunately, was useless for a good part of 

 the time, partly because its clock went out of order, partly because 

 the Sarasin gearing proyed too crude to deal with the delicate seiches 

 of Loch Earn ; and it was near the end of the time at my disposal 

 before we were able to remodel it on the plan of the waggon recorder 

 which worked so well at St. Fillans. 



Besides the limnographic apparatus, we had quite a battery of 

 meteorological instruments : three microbarographs of the Dines- 

 Shaw pattern and a Dines pressure anemograph, which was installed 

 near my house at Ardtrostan and worked beautifully. One of the 

 microbarographs was placed at Ardtrostan, one at the west end of 

 Earn, and one at Killin. At each of these places we also ran ordinary 

 barographs, which were controlled by means of bi-daily obserya- 

 tions with a standard barometer in charge of Messrs. White and 

 Watson. 



Typical Limnograms. — I will next show you some typical speci- 

 mens of limnograms obtained in yarious lakes under yarious condi- 

 tions, so that you may gather some idea of the phenomena which we 

 have to correlate, and, so far as possible, to explain. 



By the kindness of Professor Forel I am able to show you a 

 facsiuiile * of what is, so far as I know, the most remarkable seiche 

 record in existence. It is from Plantamour's limnographatSecheron 

 (near Geneva), and represents a seiche, haying a period of 78-5 

 minutes, and a maximum range of 9 inches, which lasted from 21 

 hours on March 26 to 14 hours on April 3, 1801 : that is to say, 

 7 days 17 hours. Apart from occasional wind disturbances, the 

 oscillations are very regular, as you will see. 



You may compare with this a seiche * taken with the waggon 



* Exhibited in the Lecture Room and in the Library of the Institution. 



