NOVEMDEE 13, 1908] 



SCIENCE 



671 



at the rear, however elevated the seats may 

 be, have difficulty in seeing what actually 

 takes place upon the lecture table. Should 

 the lecture room be larger than that re- 

 ferred to, the experiments must be per- 

 formed on a very large scale. This we 

 have, in a measure, obviated by placing a 

 reflectoscope on the lecture table, with 

 which experiments on a small scale may be 

 performed, and then thrown upon a screen 

 overhead. In order to accomplish this, the 

 instrument projects various objects upon a 

 mirror which reflects it upon the screen. 

 The screen can be operated to change its 

 angle so that distortion is prevented, as is 

 the practise at Cornell. 



In addition to the projection lantern 

 operated on the lecture table, to which ref- 

 erence has been made, a double dissolving 

 lantern is placed at the rear of the room. 

 A convenient method for signaling the op- 

 erator is had by means of white and red 

 lights, duplicates of which are placed with- 

 in the movable reading desk on the lecture 

 table so that the operator may signal the 

 lecturer in case there is some temporary 

 delay. Some people prefer a transparent 

 screen placed behind the lecturer with the 

 lantern operated in a room to the rear. 

 "We have provided one for such experiments 

 that utilizes the sunlight, which may read- 

 ily be reflected by a heliostat properly 

 supported without a southern window. 



LECTURE TABLE 



Many lecture rooms have the lecture 

 tables convex, which, in my opinion, is 

 wrong. Those sitting at the extreme right, 

 for example, see the apparatus head on and 

 can not observe what is really going on. 

 If the table be concave, this is obviated. 

 I do not know any lecture theater in which 

 this system has been adopted. As a matter 

 of economy in room, the straight lecture 

 table perhaps gives the best results. 



It will be recognized that the experi- 

 ments for demonstration should be selected, 

 if possible, from those which show color 

 changes or changes in volume, rather than 

 weight. Pneumatic troughs with glass 

 front and back and rear illumination have 

 given satisfaction in many laboratories. In 

 addition to these we have incorporated a 

 pneumatic trough with mercury, so con- 

 structed with an extension pipe 5 cm. in 

 diameter and 800 cm. long, that eudiometer 

 tubes, 2 em. in diameter, may be raised or 

 lowered to secure an increased or dimin- 

 ished pressure of one atmosphere. The 

 convenience of such an arrangement is 

 obvious. 



The size of the lecture table is a mattei 

 requiring grave consideration. Some of 

 the most distinguished American lecturers 

 in chemistry think that experiments should 

 be selected to show but one thing at a time. 

 This can not always be done, but necessary 

 apparatus for the experiment, as gas scrub- 

 bers, for example, may just as well be 

 placed out of sight and that part of the in- 

 stallation to which the attention of the 

 student is to be particularly directed placed 

 on the table. Despite the clarity of ex- 

 planation, students often give attention to 

 a fluid flowing into an aspirator bottle, for 

 example, instead of observing the change 

 of color in copper oxide which may be 

 heated in an atmosphere of hydrogen. 

 This principle is so emphasized by some of 

 our most experienced and expert teachers 

 that they allow the apparatus for but one 

 experiment to be placed on the table at a 

 time. That must be removed before the 

 second is begun. An elaborate array of 

 apparatus upon a long table is undoubtedly 

 theatrical in effect and may serve to catch 

 the student's attention at once and hold it 

 throughout the discourse, as he will be 

 afraid of missing a trick. This is not to be 

 depended upon, however, for the next lec- 

 ture, perhaps upon a more important topic 



