Delete!
This is a work by artists Christoph Steinbrenner and Rainer Dempf. In 2005 they covered up all advertising signs, slogans, pictograms, company names and logos in a street in Vienna for two weeks. The deletion of the information accentuates its ubiquitousness.

To See The Unseen
Andrew J Butrica’s comprehensive and revealing insight into the history of radar astronomy. For detecting and mapping of an unseen object radar technology analyses the echo received from radio signals.

Δ M i −1 = − αΣ n=1 N D i[ n][Σ j∈C[i] F ji[ n − 1] + Fext i[[ n −1]]
The spectrogram of Aphex Twin's Δ M i −1 = − αΣ n=1 N D i[ n][Σ j∈C[i] F ji[ n − 1] + Fext i[[ n −1]] reveals his face at the end of the track. A spectrogram visualises the spectrum of frequencies. With a program called MetaSynth you can insert a photo as a spectrogram and convert the picture into sound. That's what Aphex did with his face.

Unheard Sounds
This is a text I found on the website of The University of North Carolina. It's about inaudible sound. There are two different types of sound that are inaudible to the human ear, noise cancellation, and ultrasonic vibrations. The latter is sounds with a frequency higher than 20,000Hz, whereas the first is based on the concept of destructive interference.

Paolo Ucello documentary
This is a documentary about the work of the 15th century Italian painter and mathematician Paolo Ucello, whose obsessive search for the perfect vanishing point led him to become a pioneer in introducing visual perspective to painting – creating something three dimensional on a two dimensional canvas.

"I Unseen"
60s garage-psych band The Misunderstood's song "I Unseen" is based on Nâzım Hikmet Ran's poem I Come And Stand At Every Door.

Here is the poem:
I come and stand at every door
But no one hears my silent tread
I knock and yet remain unseen
For I am dead, for I am dead.

I'm only seven although I died
In Hiroshima long ago
I'm seven now as I was then
When children die they do not grow.

My hair was scorched by swirling flame
My eyes grew dim, my eyes grew blind
Death came and turned my bones to dust
And that was scattered by the wind.

I need no fruit, I need no rice I
need no sweet, nor even bread
I ask for nothing for myself
For I am dead, for I am dead.

All that I ask is that for peace
You fight today, you fight today
So that the children of this world
May live and grow and laugh and play.

Helena Hauff is featured in The Wire 354, in an article by Joe Muggs.