NATURAL PHILOSOPHY. 159 



PNEUMATO-ELECTRIC ORGAN. 



Electricity has been vei-y ingeniously and effectively applied to 

 fonu a connection between the keys of an organ and the valves 

 which permit air to pass to the pipes. Comjilicated mechanism is 

 thus got rid of, an extremely simple arrangement, whatever the 

 distance between the keys and the pii^es, being substituted. 

 According to the "Scientilic Review," when any key is depressed by 

 the finger, a small commutator under it completes communication 

 with a galvanic battery, by di^iping its lower ends into minute 

 cups of mercury. Electricity then passes along a wire to a small 

 electro-magnet, that immediately becomes excited, and, attract- 

 ing a keeper, opens a valve, allowing air to pass into the organ- 

 pipe, which sounds at once, and continues to do so as long as tlie 

 finger presses down the key. It is clear that, however powerful 

 the organ, or distant the pipes, the fingers are not in the slightest 

 degree disti'essed in playing. The battery used is simple, inex- 

 pensive, and permanent in its action. It consists of glass vessels, 

 arranged on the upper surface of the bellows, and each containing 

 a solution of sulphate of mercuiy ; into the latter plunges a plate 

 of zinc, which is placed between two plates of gas retort graphite, 

 when the bellows is raised by the action of blowing. No effect, 

 therefore, is produced, except when required, which prevents 

 waste of battery power. The zinc requires to be rej^laced, and 

 the mercury, thrown down by the zinc which is dissolved, to be 

 re-formed into sulphate, about every six months. 



SUN-SPOTS VS. MAGNETIC VARIATION. 



Father Secchi has just completed the reduction of the observa- 

 tions made during the years 1859 to 1865, inclusive, of the amount 

 of magnetic variation, on the one hand, and of the number of 

 groups of spots visible on the sun, on the other. The i-esults are 

 very interesting, as showing the intimate relation between the 

 two phenomena, — a minimum of spots invariably corresi^onding 

 to a minimum of magnetic variation. 



DEVIATION OF THE COMPASS. 



INIr. E. S. Ritchie read a paper before the Massachusetts Institute 

 of Technology, in February, 1865, on the deviation of the compass, 

 caused by the iron used in the construction of vessels, and the best 

 mode to correct it. The causes of the disturbance are : 1. The 

 presence of soft iron, which attracts equally each pole of the 

 needle, with a force nearly constant in all positions of the ship on 

 the earth's surface, and for all time. 2. The magnetism induced 

 by the earth in iron placed in or near a vertical position, causing 

 in the Northern hemisphere the lower end to become a North 

 pole, while in the opposite hemisphere it becomes a South pole. 

 3. Magnetism induced in the iron by rolling, hammering, etc., 

 during the building of the ship : this is more or less permanent 

 according to the hardness and quality of the iron ; and, among 



