SCIENCE LETTER FROM PARIS. 101 
the conditions for exploding. The same observations apply to the rest the boiler 
enjoys during the dinner hour. Thus explosions mostly occur when the opera- 
tives are resuming work. 
There is a relation between the temperature of the water and the pressure of 
the steam, hence the duty of the fireman ought to be to consult a thermometer 
and a manometer; if the two instruments disagree, the fires instead of being 
increased should be extinguished. Capt. Treve proposes that a tube be specially 
laid in the boiler, furnished throughout its length with conical apertures, along 
which the external air could be pumped; thus the water could be supplied 
with the air which it lost during the night and meal time. An electric apparatus 
could be made to communicate with the engineer's office, to register and signal 
all discrepancy between the thermometer and the manometer. 
Salmon rearing has proved a success in Paris. In 18,9 some sa'mon eggs 
were received from California and placed in the tanks or basins of the Trocadero. 
The incubation was successful ; the fry were fed on chopped whitings, and from 
half a pound weight increased to five pounds. Thus it is demonstrated that Cali- 
fornia salmon can be bred and reared in captivity under exceptional conditions, 
as change of climate and habit. It is proposed to stock the southern rivers of 
France with salmon where it is unknown. 
When one experiences a violent blow, the eye, from the effects of the shock, 
perceives an infinite number of sparks. Under certain influences the nervous 
system then experiences certain luminous vibrations. Indeed there are persons 
so sensitive that they cannot bear a sound or a noise without experiencing at the 
same time the sight of these colors. To the auditory sensation is united the 
luminous and the colored. Each sound has its peculiar color ; such a word cor- 
responds to red and another to blue, as one note may be green and another yellow. 
This phenomennon of audibleness and simultaneous vision is called " color-hear- 
ing." To Dr. Nussmaumer, of Vienna, belongs the honor of discovering the 
seeing-colors at the same moment that he perceived sounds. Others have since 
observed these colors when listening to notes of music. Equally strange, a 
melody played on a saxophone will create a yellow sensation, while on a clarionet, 
it will be red, and on a piano, blue. The compass thus of the sound exercises 
an influence on the phenomena. The energy of a sound corresponds to the 
intensity of color. The most brilliant silver-white colors accompany the shrillest 
whistle. The human voiqp determines a multiplicity of impressions: thus the 
vowels / and e produce on emission the most lively colors : a and shades less 
brilliant, while u has a sombre tint. It is a curious fact that individuals who 
can thus perceive the colors of sounds fail to recognize those of their own voice. 
Major Joufifret in his volume on the "Theory of Energy" states, that it is 
completely impossible for us to know the veritable essence of atoms ; all we are 
certain of is that they are not immovable, that each molecule resembles a little 
solar system or like nebula in constant agitation. What is meant by the tenuity 
