A HOME-MADE SPECTROSCOPE. 



811 



Fasten the lower strip of the two permanently to the disk, leaving 

 the other strip free to move in an horizontal plane about the center of 

 the disk. You will then have a stand like that represented in Fig. 3, 



A being the stationary arm, and B the movable arm. Make the small 

 disk of wood also into a table (see Fig. 4) by fastening in three sharp 

 feet screws will do. Place this smaller table centrally on the larger 

 one, and it becomes the platform on which the 

 prism is to stand. The next thing is to put the 

 collimator and telescope in their places. For 

 this purpose two small oblong blocks of wood 

 are needed, each one having the upper part 

 hollowed out into a groove to take one the 



collimator, the other the telescope. (See Fig. 5, d, d.) The block 

 carrying the collimator is placed on the stationary arm, and the one 

 with the telescope on the arm which is free to move. Both are se- 

 cured in their places by elastic bands. The blocks of wood must 

 necessarily be of such a height that the axis of their respective tubes 

 (collimator and telescope) may be brought into alignment (1) with 



FicfA. 



Fjct.5. 



each other, and (2) with the prism. The instrument is then complete 

 (see Fig. 5), where A is the collimator, JB the prism, and C the tele- 

 scope. , 



The manner of using the spectroscope has been described in such 

 works as those I have already mentioned, and does not properly be- 

 long to an article such as this, but perhaps a few hints as to the ad- 

 justment of the instrument 'may not come amiss to the beginner. The 



