NEW FORM OF ANEMOMETER. 39 



impurities contained in the smoke-black, or in the alcohol used to lay 

 it with a brush on the surfaces of the paddles ; and as pulverized coal 

 condenses vapours with an energy that is well-known, it is impossible 

 to avoid coming to the conclusion that the vacuum produced by 

 Sprengel's pump is by no means perfect. The pressure of the gases 

 which have not been removed varies according to circumstances, and 

 it is to the different degrees of this pressure that we must attribute the 

 various motions of the instrument invented by Mr. Crookes. 



The PRESIDENT : I do not know whether Mr. Crookes is present, 

 but we should have been very happy to have heard anything from 

 him on this subject, which has excited so much interest both here and 

 on the Continent. If there is any other gentleman present who has 

 any remarks to offer we shall be very pleased for him to do so. 



I am afraid Lord Rosse, who had promised to take a part in this 

 Conference, has been prevented by some means from coming, but Mr. 

 Fletcher is here, and he will give us an account of his Anemometers. 



Mr. FLETCHER : When an effort was made to examine chemical 

 works with a view to carry out the provisions of the new Alkali Act it was 

 found necessary to measure the amount of vapour, gas or smoke which 

 was passing along the flues which entered the chimneys of the works, and 

 as a first step it was necessary to find out the speed at which the gases 

 were passing along. As there was corrosive vapour and soot, and in 

 many cases flame passing with the air, it was impossible to use the 

 ordinary Anemometer consisting of delicate mechanism of various 

 kinds, a light fan wheel passing round and the revolutions being 

 counted by delicately poised wheels. Of course, such an instrument 

 once introduced into a flue which was red hot would not shew any very 

 accurate indications when it came out again, therefore this Anemometer 

 was devised to answer the purpose which was wanted. It consists of 

 two tubes of ordinary gas piping which may be of any length. 

 One is bent at right angles, and the other is cut of short. They are 

 passed through a hole in the brick work and thus introduced in the 

 current of gas. If the vapour is passing upwards the bent one would 

 be turned down so as to receive the pressure into its open end, whilst 

 the other one is crossed by the current. The action in the open one 

 is to experience a slight vacuum or exhaustion, and a slight pressure 



experienced in the bent one. By flexible tubing the other ends of 



