Faraday to Jacob Herbert   29 August 1853

Royal Institution | 29 Aug. 1853

My dear Sir

In consequence of your letter regarding the Cromer lighthouse¹ and our conversation in your room I proceeded to the place and was there examining into the circumstances & condition both by day & night on the 23rd & 24th instant²: & will now give you briefly the results, which are included chiefly under two heads the ventilation & the warming of the lanthorn.

The ventilation appears to have been much cared for & presents rather a complicated system. There are eight circular ventilators in different places in the stone work of the lower part of the lanthorn. They are moderate in size & the perforations in the surface plate are such that each offers an air way of 5 1/2 square inches. They are good as far as they go but are few in number & small in size; supposing the lanthorn depended chiefly on them. Then there are twenty small ventilators, opening, one under each lower pane of glass & directly in front of it; each has an air way of 18 2/3 of a square inch. These as they come into action under the influence of the wind are very useful on the windward side of the lanthorn. Further there are Eleven tubes above which being partly open to the outer air at their origin above the glass, then go upwards near the enclosed roof for a distance of 4 1/2 feet[.] They are 3 inches in diameter. I suppose it is imagined that streams of fresh air entering by them will tend to propell the bad air out of the top at the cowl. They are of no use where they are for only the two or three to windward will ever have air entering by them; that air will have no more ejecting force over the bad air than if it entered below; & entering above it is lost as fresh air to the lighthouse. What little effect they have is more hurtful than good.

A most important adjunct to the ventilation exists in the Watch room windows. These are three in number being on the North East & West sides. They are 45 inches wide each, and the sashes open from above. The watch room is a very dry room. The tower itself also is dry but no air enters the lanthorn or watch room from below. Some of the brethren directed the keepers attention to the use of these windows in aiding ventilation; and since then the difficulty which occurred on special occasions of extreme cold or closeness has been removed: they have but to open the windward window more or less to keep the glass perfectly clear & the lanthorn in a right condition as to ventilation[.]

As I am about to propose to take the Eleven upper tubes down on the first convenient opportunity I will here enter into a brief explanation of the action of the many ventilators in this lanthorn: in fact the principles & effects concern all lanthorns being general in their nature. It might have been thought that thirty nine ventilators were enough for one lanthorn; but of this number, when all were open, only nine passed the fresh air inwards. I examined the currents through them again & again both at day & night time: the results were constantly the same. Of the eight larger ventilators only the two to windward admitted constant streams of air: the other six had varying currents i.e in & out but chiefly outwards. Of the twenty small ventilators only the four to windward gave constant entering currents, the two or three to leeward passed the air in & out irregularly; the 13 or 14 others gave a constant & strong current outwards[.] This is the natural effect of the wind acting on their hoods it is the same as that which I have found on former occasions at the Needles & elsewhere and is due to the principle which acts so beneficially in the wind guard. Of the Eleven upper ventilators air entered at the three to windward, but the other eight passed more air outwards than inwards[.] If it be now considered that the joint air passage of the 2 larger and 4 smaller ventilators giving access to air in the lower part of the lanthorn is only 18 square inches it will be understood how much additional aid is gained by the use of the watch room windows. If the window to windward be opened only one inch it offers a passage to air having an area of 45 square inches and as an equal aperture is opened between the upper & the lower sashes by the same act, 90 square inches of sectional area or of air passage is there, at once obtained. This amounts to five times that of all the ventilators which supply fresh air to the lamps & glass at the same time[.]

There appears to be plenty of air way out at the Cowl, provided air be let in below as described. The ventilation of the lamps is also perfect according to the description of the keepers & the action at the time that I saw it. Before the lamp tubes were put up, there was a continual condensation on the roof and droppings from the ribs. To remedy the dropping evil, a collecting gutter was put up against the ribs and a pipe from it conducted the condensed water into a vessel placed beneath[.] The keepers say that now there is no condensation on the roof nor do they ever have to place the vessel into which the water formerly ran. If this be really so on the most cold & trying nights then the gutter might as well be taken away with the eleven pipes before referred to, on any convenient opportunity[.]

Proceeding to the warming of the lanthorn; I find that the keepers complain of its temperature in cold weather. They state that the oil in the lower lamps then freezes: that they cannot make those lamps burn properly either by turning up the cottons or otherwise; that the oil will not freely descend to the cotton; & that on such occasions the quantity burnt in a lower lamp has not been more than two thirds of that burnt in an upper lamp for the same time. I can well understand this to be the case especially with the Rape oil[.] After the lamps are lighted the temperature is very different indeed in the upper & the lower parts of this fine high lanthorn. I found it so, and they say the difference is quarter in the cold weather. To counteract this effect there is a stove in the watch room. It has a jacket, from which the hot air passes by a pipe 6 1/2 feet long & only 3 inches in diameter into the lanthorn at one place in the floor. The chimney of the stove which in the watch room is 6 inches in diameter passes through the floor into the lanthorn & is then continued upwards as a copper pipe 10 inches in diameter & 13 1/2 feet long & then goes out through the roof. This stove is insufficient in time of need. They have had to make such large fires in it as seem to burn it out, and now when the fire is lighted the smoke enters into the air chamber & so into the lanthorn. They have had occasion to heat the stove so highly that the part of its chimney in the lanthorn has been dull red hot. The stove must then have done duty far more by the hot chimney in the lanthorn & by the warming of the air in the watch room than by the small supply of hot air which its pipe of 3 inches in diameter could convey: but such a kind of action forces the stove too far, & by burning it out soon causes its derangement.

I am fully persuaded that the presence of a simple stove in the lanthorn, without air jacket and with a horizontal flue, will be far more effectual than the present stove and burn far less fuel. The place is well fitted for an arrangement like that at the St. Catherines light where the horizontal part of the flue runs under the gallery[.] At Cromer the platform is 18 inches wide. There is a corner under the gallery at the head of the stairs which would do exceedingly well for the stove; the distance from it to the present place of the chimney is in one direction under the gallery 26 feet & in the other direction about 11 feet[.] I would recommend that the present upright chimney be replaced by one terminating above with a wind guard as at St. Catherines (See report of 29 June 1853³.); that the horizontal part of the chimney kept at about an inch from the wall & from the platform be continued from the stove to this upright part in both directions; & that near the entry into the upright part there be throttle valves that either the one length or the other, or both may be used according to circumstances. In the vertical part of the chimney, the upper lengths should be put into & not over the lower length, as described in the report just referred to; & there should be a vessel termination to collect any condensation in this part[.]

The keepers at this house are remarkable for their practical sagacity: they have by observation & experience discovered several points in the working of the lights & lighthouse which are fully justified by principle & well illustrate it. They in this respect form a very striking contrast to some other establishments which I have visited[.] The lighthouse both by day & night presents an object well worthy of approbation[.]

The flag staff N has been set I suspect by a magnetic needle without the card; it is 20˚ or more west of the North star⁴[.]

I am | My dear Sir | Ever Your faithful Servant | M. Faraday

Jacob Herbert Esq | &c &c &c