Book about May Day Howie reads in the library
There are three texts associated with this scene. At this point, it appears that they are all separate items. It is possible that texts 2 and 3 are from the same source. The first book cannot be source #2 as #2 was published in 1972 but not with marbled edges.
source #1)The first is the antique book that has marbled edges that we see in the medium shot of Howie reading it.
source #2) The second is seen in close-up. This is the book published in 1972, Mysterious Britain by Janet & Colin Bord. We see the beginning of chapter 13 : "Britain: Land of Legends. The first sentence starts: "Britain, the Isle of the Blest of the early chroniclers... " The second paragraph starts: "Dragons feature in legends from all parts of the world and..." The third paragraph starts: "On the banks of the River Wear in Durham..." (The picture of the betty, hobby, fool and sword lock facing this page have not been seen in the edition I've read but might in other editions. It could very well be from another source.)
source #3) The third text is what we hear Howie reading. Much of it is similar to what Shaffer had scripted (see his script (pdf)) in scene #98 which never made it into any version. (Was it shot?) That text is below. (I am uncertain how it should be formatted... It could be contiguous. We don't know at this point.)
Steve P says "there is evidence that the words Howie is "reading" were mostly scripted during post-production, and recorded during the ADR (Additional Dialogue Recording) phase." (Possibly from a cut scene involving Miss Rose where Howie asks her about May Day. Sc 98 in the Pitt script.)
"Primitive man lived and died by his harvest. The purpose of his spring ceremonies was to ensure a plentiful autumn. Relics of these fertility dramas are to be found all over Europe. In Great Britain, for example, one can still see... harmless versions of them danced in obscure villages on May Day. Their cast includes many alarming characters: A man-animal, or hobbyhorse, who canters at the head of the procession charging at the girls; A man-woman, the sinister teaser, played by the community leader or priest; And a man-fool, Punch, most complex of all the symbolic figures - the privileged simpleton and king for a day. Six swordsmen follow these figures... and at the climax of the ceremony lock their swords together... In a clear symbol of the Sun. In pagan times, however, these dances were not simply picturesque jigs. They were frenzied rites ending in a sacrifice by which the dancers hoped desperately to win over the goddess of the fields. In good times, they offered produce to the gods and slaughtered animals, but in bad years, when the harvest had been poor, the sacrifice was a human being. In some cultures, it would be the king himself. In others, the most beloved virgin. Very often he or she would be kept hidden for months preceding the ceremony, just as the Sun is hidden from the Earth in winter. Methods of sacrifice differed. Sometimes the victim would be drowned in the sea... or burnt to death in a huge sacrificial bonfire.
Sometimes the six swordsmen ritually beheaded the virgin. The chief priest then skinned the child, and wearing the still-warmed skin like a mantle, led the rejoicing crowds through the streets. The priest thus represented the goddess reborn and guaranteed another successful harvest next year."
The Pitt script says that the book Howie reads in the library is an encyclopedia, the volume for "H" and that the chapter is on Harvest Festivals...
Calendar in the darkroom
The text for the page for May reads:
… of Aroochar ? around the waters of
On the right is Ben Lomand 3192'
? ? in Dunbartonshire.
The covered chair Lord Summerisle sits in when Howie enters the room
The covered (canopied) chair that Lord Summerisle is sitting in when Howie first enters the room was once part of a carriage and is hundreds of years old, belonging to the Stair Estate. (See Nuada #3, What the Butler Saw article.)
Ingrid Pitt's bath
A similar bathtub can be found at the The Museum - Newton Stewart! Here's a pic:Note though that this bathtub has handles on each side. The one Ingrid sat in does not. (NSFW pic)
John Barleycorn bread
"This is a picture of a picture that was/is on display in Creetown Museum and supplied by a local - possibly Mickey Harvey who owned the bakery location. I don't think it was real bread. The sun loaves were polystyrene as they had to be taken to a few locations much like Mr Barleycorn." (Declan McCafferty, Facebook.) In the movie, you can see the coffin-shaped tin better.
Lawnmower the gravekeeper uses
A list of all the masks used and who wears them.
Map outside of Ingrid's bath
This appears to be a map of the Aegean Sea.
Only seen in the Director's cut.
A Vilida Supa-Mop held by the gravekeeper and perhaps others as the villagers line the crest and dismask with Howie below at the cliffs. Also a large brown book held by the man who took the pictures at the Chop Chop scene (not Lennox). Another appears to hold a black hobby horse.
Police car on the mainland
The police car Howie and McTaggert ride in, in the long version, is a 'Newcastle-registered police Mini Panda', according to this web page. Here's  the brightest shot I've ever seen of a c/u of them in it.
Here's another site with more than you want to know about it...
Pony trap Howie rides to Lord Summerisle's castle
It is a "Governess cart." One "cannot tell the maker without looking at hubs etc." - Ruaridh Ormiston of the Scottish Carriage Driving Association Ltd. It was owned by the Stair Estate.
And this pic .
Rowboat with the evil eye
The small boat which the harbour master uses to row Sgt Howie to and from his plane was actually called The Escampador and belonged to one of the fishermen in the film. This boat was based at Plockton where it remained until 2004 when it was sadly destroyed in a storm. (Shaffer website) Mary Gollan of the Plockton Inn: "She did indeed meet her end being wrecked. She had been upside down for a while and had been turned the right way up in preparation for a move down to the south coast of England for refurbishment and that same night a storm came and she was swept away."
The eye would be called Bel, from Beltane? (Quite common on fishing boats in the Mediterranean, but not a British tradition.)
Sailing ship that Howie searches ("Schooner Summerisle" - Brown)
This was the schooner Captain Scott. She was built in 1971 and used for training kids about seamanship. There are some movies from that time, info and movie here and launching here. The footage of her in the harbor and the inspection was shot on October 9 and/or 10, 1972.
Her distinctive figurehead (of Captain Scott with cap and goggles) is shrouded in the movie and a more typical female one added below it.
In 1977 she was sold to Sultan Qābūs bin Sa‘īd of Oman where she was renamed Shabab Oman, which can be translated as "Youth of Oman." (Wikipedia)
According to locals the boat, which we see during the search for Rowan, served in the Gulf War! Whether it was delivering apples to the troops is unknown. (wicker-man.com, circa early 2000s)
The airplane Howie flies is a Thurston TSC-1A Teal. It met its end when it had engine trouble, had to land in a field and was vandalized. More info on it here. It was owned and flown in the aerial sequences by Christopher Murphy.