110 REPORT — 1851. 



the village of Settle I detected some cases nearly identical with many of the cretins 

 of the Alps. In the village of Chiselborough in Somersetshire, most of its 350 in- 

 habitants are afflicted with goitre, are very subject to deafness, imperfect utterance, 

 and low degree of intelligence, which in as many as 24 individuals descends to 

 absolute cretinism." Idiotcy is generally allowed to be incurable, whilst cretinism 

 has been often cured, yet in all cases idiots are capable of some kind of amelioration. 

 This has been proved by Dr. Howe of Boston, United States, and the three insti- 

 tutions founded within the last few years in this country. At Park House, Highgate, 

 and at the branch institution at Essex Hall, Colchester, great relief has been afforded 

 and beneficial change effected in the state of the poor idiot children in regard to 

 health, behaviour, happiness, comfort, and even intelligence, for in many cases they 

 have been enabled to occupy themselves in various useful ways. The work of re- 

 storing the cretins has been carried on in Switzerland by one devoted individual 

 during the last ten years. Similar establishments are now rising up in several parts 

 of the continent. Three houses have been opened in this country for the poor idiot, 

 but the number of applicants far exceeds the vacancies ; to ascertain the numbers, 

 and to provide institutions, is now a work to be carried on, every effort hitherto made 

 having proved successful as far as the nature of the case admitted of relief or cure. 



In the discussion on this paper, Mr. Kennedy (Director of Statistics at Washington) 

 pointed out that in the last United States Census, the name and residence of every idiot 

 in the States was recorded, so as not only to show the number of idiots, but also to 

 give to charitable institutions the means of relieving them. Mr. J. Hancock and 

 Mr. Gowing also took part in the discussion. 



A Mathematical Exposition of some Doctrines of Political Economy. 

 By the Rev. W. Whewell, M.A., D.D., F.R.S. 



MECHANICAL SCIENCE. 



On the Duplex Rudder and Screw Propeller. By Capt. Carpenter. 



The models represent views of a screw steamer constructed on what, after much 

 consideration, I have determined to call the duplex princiijle, namely, with two rud- 

 ders and two propellers for improved steering and propelling. To construct a vessel 

 on this plan, the dead wood, stern-post and rudder are removed from their former 

 position, and the midship keel, which before was placed in a straight and horizontal 

 line from stem to stern, is now made to rise up on a graduated scale from the mid- 

 ship section to the water-line of the midship part of the stern, where it terminates. 

 The additional keels lie in a parallel line with the midship keel, but placed at a di- 

 stance of two or more feet, according to the size of the vessel, on either side of it, 

 terminating near to the midship section in the fore-part, and in a line with the former 

 stern-post in the after-part. A stern-post is placed at the end of the additional keels, 

 and upon each of them hangs a rudder. Framework is carried down to these keels 

 in proper architectural lines for speed, at the same time connecting the frame together, 

 so that the strength of the vessel is increased in the after section, where it is most 

 required in a screw steamer. Between this framework, a channel is formed for the 

 water to pass away freely in a direct line with the midship keel. A screw propeller 

 works in an orifice in each framework on the common arrangement. One of the 

 propellers is a little more aft than the other to allow fullplay to both, and yet eco- 

 nomize space in the mid- channel. The propellers turn each of them towards the 

 centre line of the vessel for propelling and the reverse way for backing. A steering- 

 wheel is placed on the deck in the usual way, and connected with the tillers, which 

 move the rudders together in parallel planes, or separately, as may be required. The 

 propellers can be lifted out of the water, for sailing, by means of a simple appara- 

 tus, which is placed on the deck for that purpose, or they may be feathered if pre- 



