106 proceedings of sectiox a. 



Friday, August 31. 

 The President, Mr. R. L. J. Ellery, F.R.S., in the Chair. 



The following papers were read : — • 



1.— EXHIBITION OF A MODEL FOR FINE DISTANCE 



ADJUSTMENTS. 



By H. C. Russell, B.A., F.R.S., Government Astronomer. 



\^Ahstract.^ 



Mr. Russell exhibited a model illustrating the nicety with 

 which distance adjustments can be made by the aid of an electrical 

 contact ; even with a very rough arrangement the point of conta'ct 

 was quite definite within about 3-77,^73 of an inch. Mr. Russell 

 gave a description of some apparatus for continuously registering 

 the direction of the vertical, and based on the property above 

 described. 



2.— A PROPOSED METHOD OF RECORDING VARIA- 

 TIONS IN THE DIRECTION OF THE VERTICAL. 



BY 



H. C. Russell, B.A., F.R.S., Government Astronomer. 



Nearly eighteen years since I introducd into the Sydney 

 Observatory a Barograph, which records the variations in the 

 atmospheric pressure by means of an electric contact, and I have 

 often been surprised at the extremely minute changes which it 

 will record. But it was not until the other day that it occurred 

 to me that a modification of the same method would record 

 changes in the direction of the vertical, and I, thereupon, 

 arranged one of the Micrometer Microscopes, so that the motion 

 of the screw brought the two ends of an electrical circuit into 

 contact. I made a great number of experiments myself, and 

 found that contact was always made when the pointer shewed 

 the same place on the divided head of the screw ; certainly 

 within j-Lq of a division which is within ^-o.^nro^ ^^ ^^^ inch. Two 

 assistants then at my request and at difierent times tried the same 

 experiment, without knowing what had been done, one got 

 exactly the same result]^as mine, the other thought contact safe 

 within less than 75-0,^0-0- A larger graduated head was then 



