346 Dr Grant on the hifluence of Light 



that the bulb be actually inserted in the magazine which con- 

 tains it, and the stem being turned down, should run parallel 

 to the instrument, the degrees running downwards, which is 

 actually the direction they assume on the lower scale upon 

 which that of inches and fathoms slide. Farther, though 

 this I think would nearly obviate the evil, the bulb of the 

 mercurial thermometer might advantageously be made much 

 smaller, and a very minute hut flattened bore applied. Thus the 

 degrees would be rendered smaller ; but if they were only half 

 their present size, the accuracy, I am convinced, would be ad- 

 vantageously transferred from the minuteness of the adjust- 

 ment of the scale to the certainty that that adjustment, as 

 nearly as it could be made, would be in its principle correct. 

 A nice eye would discern the tenth of a degree if aided by 

 skilful graduation, though no larger than half what they 

 are at present, and a lens might even be provided. The ma- 

 gazine of hydrogen should also be more defended than at pre- 

 sent from the influence of the breath of the observer ; and even 

 were the position of the thermometer not to be altered, the se- 

 clusion of the gaseous bulb from the more immediate action of 

 atmospheric changes, would be advantageous, by rendering it 

 more similar in condition lo the mercury. Other precautions 

 will doubtless occur to practical men, for the remedy of the 

 defect I have endeavoured to prove, if my deductions be correct. 

 In conclusion, I have only to observe, that my animadver- 

 sions of course apply to the sympiesometer merely as used in 

 the measurement of heights ; as a marine barometer, its supe- 

 riority in accuracy and utility, as well as convenience, seems 

 fully established. 



Aet. XXIII. — On the influence of Light on the motions of 

 Infusoria. By R. E. Gkant, M. D., F. R. S. E., F. L. S., 

 Professor of Zoology and Comparative Anatomy in the Uni- 

 versity of London. Communicated by the Author. 



\ Many animals appear sensible to the impression of light which 



^ have obviously no distinct organs of vision, and some even 



which exhibit no trace of a nervous system are notwithstand- 



